&#34;Solar Mirrors and Methods of Making Solar Mirrors Having Improved Properties&#34;

ABSTRACT

An article for reflecting solar energy includes a coating stack having solar reflecting films and metal oxide films, the coating stack applied on a major surface of a glass substrate, and a protective overcoat comprising a first and a second surface, wherein the first surface of the protective overcoat is disposed toward the solar reflective films and metal oxide films; and a polymer encapsulant over outer wall surfaces of the coating stack, the second surface of the protective overcoat and over peripheral edges of the coated article, the encapsulant having a base layer, a top layer and metallic corrosion-inhibitive material in the base layer.

CROSS REFERENCE TO REPLATED APPLICATION

This application claims the benefits of U.S. Provisional PatentApplication Ser. No. 62/219,386 filed on Sep. 16, 2015 and titled “SOLARMIRRORS AND METHODS OF MAKING SOLAR MIRRORS HAVING IMPROVED SELECTEDPROPERTIES”. This application further is a divisional of, and claims thebenefit of, U.S. patent application Ser. No. 15/208,778, which was filedon Jul. 13, 2016 and titled “SOLAR MIRRORS AND METHODS OF MAKING SOLARMIRRORS HAVING IMPROVED PROPERTIES”, and which was published on Mar. 16,2017 as United States Patent Application Publication No. 2017/0075045A1. U.S. Provisional Patent Application Ser. No. 62/219,386, U.S. patentapplication Ser. No. 15/208,778, and United States Patent ApplicationPublication No. 2017/0075045 A1 are incorporated herein by reference intheir entireties.

NOTICE OF GOVERNMENT SUPPORT

This invention was made with Government support under Contract No.DE-FC36-08GO18033 awarded by the U.S. Department of Energy. The UnitedStates Government may have certain rights in this invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This application relates to articles for reflecting electromagneticenergy, especially electromagnetic energy emitted by the sun. Thearticle includes but is not limited to solar mirrors and to methods ofmaking solar mirrors having improved physical properties, e.g. but notlimited to spectral properties to increase the usable life andperformance of the solar mirror.

2. Presently Available Technology

As is appreciated by those skilled in the art of solar mirrors, solarpower is becoming a more commercially acceptable and economically viablesource of energy. By way of example and not limiting to the invention, aknown application is using solar mirrors to concentrate solar light forelectrical generation. As used herein, the term “solar light” meanselectromagnetic energy emitted by the sun. Solar mirrors having highreflectance of solar radiation are used for “concentrated solar thermalpower (CSTP) installations. There are several different mirrorgeometries used for these applications. One system uses curved parabolicsolar mirrors to concentrate solar energy onto tubes positioned along afocal line. A heat transfer medium in the tubes carries the absorbedheat energy to a generator station where it is used for powergeneration. Another system uses a solar tower in which solar mirrorsreflect and concentrate solar light onto a receiving surface on thetower. The heat generated by the focused solar light is transferred to aworking fluid, such as sodium, and the heated working fluid is used forpower generation.

Another application of such mirrors is for “concentrated photovoltaics”(CPV). in this application, mirrors focus or concentrate solar lightonto photovoltaic (PV) devices, thereby improving the energy output perdevice.

In these systems, and as discussed above, it is desirable that themirrors reflect as much solar light as possible, it is also desirablethat the mirrors have as long a commercial life as possible to precludefrequent changing of the mirrors. Mirrors having a reflective surfaceare used to reflect solar energy to a focal point having the devices toconvert solar light or energy to electric and/or thermal energy. In thepractice of one non-limiting embodiment, the solar mirror includes aglass substrate having a first major surface and an opposite secondmajor surface. The first major surface is designated to face the sourceof solar light, and the opposite second major surface of the glasssubstrate faces away from the source of solar light. In thisnon-limiting embodiment, a reflective coating is applied over the firstmajor surface of the substrate. In another non-limiting embodiment ofthe invention, the reflective coating is applied over the second majorsurface of a light transmitting or transparent substrate, in thefollowing discussion, the solar reflecting mating is applied over thesecond major surface of the transparent substrate. The second majorsurface faces away from the so of solar light or energy.

Further as is appreciated by those skilled in the art of solar mirrortechnology, it is desirable to maximize the amount of solar lightreflected from the solar minor and to maximize the useable service lifeof the solar mirror. The percent reflection of solar light from thesolar mirror is equal to the irradiance of solar light reflected fromthe solar mirror divided by the irradiance of solar light incident onthe solar mirror. The reflectance can be measured in any convenientmanner, e.g. but not limited thereto, the reflectance of solar light inthe practice of the invention was measured using a spectrophotometer.

Disclosed herein are methods and articles to increase the percentreflection of solar light from a solar mirror, and increasing theuseable life of the solar mirror.

SUMMARY OF THE INVENTION

This invention relates to an article for reflecting solar energyincluding, among other things a substrate having a first surface and anopposite second surface, and a solar reflective coating. The solarreflecting coating including, among other things, a first metal solarreflecting film hereinafter also referred to as the “first metal film”,the first metal film having a first surface and an opposite secondsurface; a second metal solar reflecting film hereinafter also referredto as the “second metal film”, the second metal film having a firstsurface and an opposite second surface, and a parting layer or filmhaving a first surface and an opposite second surface, wherein the firstsurface of the parting film is over the second surface of the firstmetal film and the first surface of the second metal film is over thesecond surface of the parting film, wherein the first surface of thefirst metal film is over and attached to the second surface of thesubstrate.

The invention further relates to an article for reflecting solar energy,having, among other things, a coating stack having among other things,solar reflecting films and metal oxide films, the costing stack appliedon a major surface of a glass substrate; and a polymer encapsulant overouter wall surfaces of the coating stack, the second surface of theprotective overcoat and over peripheral edges of the coated article, theencapsulant including, but not limited thereto, a base layer, a toplayer and metallic zinc flakes in the base layer.

The above mentioned article further includes marginal edge portions ofthe top of the mating stack and the outer walls of the coating stackcovered with the base layer and the base layer defines an uncoated areaon the top surface of the coating stack, and the top layer overlays thebase layer and the uncoated area of the top surface of the coatingstack.

The invention still further relates to an article for reflecting solarenergy, including, among other things, a coating stack secured to majorsurface of a glass substrate, the coating stack, comprising a solarreflecting layer, wherein the surface of the coating stack spaced fromthe substrate is electrically conductive, and a polymer encapsulant overouter wall surfaces of the coating stack, the encapsulant comprising atop layer eleotrodeposited (also known as “electrocoated”) to the outersurface of the coating stack. wherein the base layer of the encapsulantemploys metallic zinc flakes.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a prior art solar reflecting mirrorshowing the solar reflecting coating.

FIG. 2 is an isometric view of a prior art shaped solar mirror showingan enlarged view of a sun's ray incident on the concave surface of thesolar mirror.

FIG. 3 is a view similar to the view of FIG. 1 showing a solarreflecting mirror of the invention having the solar reflecting coatingof the invention.

FIG. 4 is a view similar to the view of FIG. 3 showing anothernon-limiting embodiment of a solar reflecting coating of the invention.

FIG. 5 is a view similar to the view of FIG. 1 showing another prior artembodiment of a solar mirror having additional coatings. Cross hatchingnot shown in FIG. 5 for purposes of clarity.

FIG. 6 is a view similar to the view of FIG. 5 showing the solarreflective coating of the invention with the additional coatings andfilms of FIG. 5. Cross hatching not shown in FIG. 6 for purposes ofclarity.

FIG. 7 is a graph showing approximate specular-excluded solar-weightedRg reflectance (“SpEx WIRg”) of a prior art solar reflecting mirror anda reflecting mirror of the invention.

FIG. 8 is a graph showing approximate specular-excluded solar-weightedRg reflectance (SpEx WIRg) of Samples 3a and 4a with their coating inthe as deposited, unheated condition, and of Samples 3b and 4b withtheir coating in the deposited heated condition.

FIGS. 9-13 are views similar to the view of FIG. 3 showing non-limitedembodiments of encapsulant having an encapsulation in accordance to theteachings of the invention.

FIG. 14 is an isometric view of a flat solar reflecting mirrorincorporating features of the invention.

FIG. 15 is a view taken along line 15-15 of FIG. 14.

DESCRIPTION OF THE INVENTION

As used herein, spatial or directional terms, such as “left”, “right”,“inner”, “outer”, “above”, “below”, and the like, relate to theinvention as it is shown in the drawing figures, However, it is to beunderstood that the invention can assume various alternativeorientations and, accordingly, such terms are not to be considered aslimiting. Further, as used herein, all numbers expressing dimensions,physical characteristics, processing parameters, quantities ofingredients, reaction conditions, and the like, used in thespecification and claims are to be understood as being modified in allinstances by the term “about”. Accordingly, unless indicated to thecontrary, the numerical values set forth in the following specificationand claims can vary depending upon the desired properties sought to beobtained by the present invention. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical value should at least be construedin light of the number of reported significant digits and by applyingordinary rounding techniques. Moreover, all ranges disclosed herein areto be understood to encompass the beginning a ending range values, andany and all subranges subsumed therein. For example, a stated range of“1 to 10” should be considered to include any and all subranges between(and inclusive of) the minimum value of 1 and the maximum value of 10;that is, all subranges beginning with a minimum value of 1 or more andending with a maximum value of 10 or less, e.g., 1 to 3.3, 4.7 to 7.5,5.5 to 10, and the like. Further, as used herein, the terms “formedover”, “deposited over”, or “provided over” mean formed, deposited, orprovided on but not necessarily in direct contact with the surface. Forexample, a coating layer “formed over” a substrate does not preclude thepresence of one or more other coating layers or films of the same ordifferent composition located between the formed coating layer and thesubstrate.

As used herein, the terms “polymer” or “polymeric” include oligomers,homopolymers, copolymers, and terpolymers, e.g., polymers formed fromtwo or more types of monomers or polymers. The terms “ultravioletregion” or “ultraviolet radiation” mean electromagnetic energy having awavelength in the range of 100 nanometers (hereinafter “nanometer” alsoreferred to as “nm”) to less than 380 nm. The terms “visible region” or“visible light” refer to electromagnetic radiation having a wavelengthin the range of 380 nm to 780 nm. The terms “infrared region” or“infrared radiation” refer to electromagnetic radiation having awavelength in the range of greater than 780 nm to 100,000 nm. Also,parameters such as “visible transmission” and “visible reflection” andthe like are those determined using conventional methods. Those skilledin the art will understand that properties such as visible transmissionor visible reflection can yaw based on the physical dimensions, e.g.,thickness, of the article being tested. Therefore, any comparison to thepresent invention should be calculated at an equivalent thickness.

Before discussing several non-limiting embodiments of the invention, itis understood that the invention is not limited in its application tothe details of the particular non-limiting embodiments shown anddiscussed herein since the invention is capable of other embodiments.Further, the terminology used herein to discuss the invention is for thepurpose of description and is not of limitation. Still further, unlessindicated otherwise, in the following discussion like numbers refer tolike elements.

Non-limiting embodiments of the invention are directed to solar mirrors.As can be appreciated, the solar mirror ea be a flat solar mirror, e.g.but not limited to the prior art flat solar mirror 5 (FIG. 1) and/orflat solar mirror 7 incorporating features of the invention (FIG. 3), ora shaped solar mirror, e.g. but not limited to shaped solar mirror 9(FIG. 2) having a concave surface 10 and an opposite convex surface 11and discussed in detail in United States Published Patent Application2010/0242953 (hereinafter also referred to as “Pub, '953”), Pub '953 inits entirety is hereby incorporated by reference.

Non-limiting embodiments of the invention are discussed with referenceto the reflection of electromagnetic radiation, such as, but not limitedto, electromagnetic waves having wavelengths in the range of 300-2500nm. As used heroin, the term “reflective article refers to any article,e.g. but not limited to “solar mirrors” configured to reflectelectromagnetic radiation, such as ultraviolet, visible, and/orinfrared, radiation, e.g., for use in concentrated solar power systems.However, it is to be understood that the embodiments of the inventionare not limited to use with solar mirrors, but could be practiced witharticles in other fields, such as but not limited to laminated ornon-laminated residential and/or commercial minors, and/or windowsand/or reflectors for optical systems (e.g., video projectors or opticalscanners), just to name a few. Therefore, it is to be understood thatthe specifically disclosed exemplary embodiments are presented simply toexplain the general concepts of the invention and that the invention isnot limited to these specific exemplary embodiments.

The non-limiting embodiments of the invention to be discussed hereininclude, but are not limited to (A) a solar reflective coating havingimproved optics and stability; and (B) an encapsulated coating stack ofa solar mirror to increase useable life of the solar mirror. In thefollowing discussion, the coating stack of the solar mirror employsmagnetron sputtered vacuum deposited solar reflective films, layers andcoatings. The invention, however, is not limited thereto, and theinvention can be practiced with any type of deposited film, layer and/orcoatings, e.g., chemical vapor deposition coating process. It isunderstood that the embodiments of the invention are presented inseparate identified sections for an appreciation of the non-limitingembodiments of the invention and not to indicate in one form or anotherthat the embodiments of the invention are independent and distinct fromone another. As is appreciated, the non -limiting embodiments of theinvention can be used alone or in combination with one another.

Solar Reflective Coating Having Improved Optics and Stability

This non-limiting embodiment of the invention provides a solarreflective coating and a method of applying the solar reflective coatingto a substrate to provide a solar mirror having improved optics andthermal stability compared to the solar mirrors of the prior aft Priorart solar mirror 5 shown in FIG. 1 includes a substrate or ply 12 havinga first major surface 14, i.e. an outer major surface 14, and en opposedsecond major surface 16, or inner major surface 16. The solar mirror 9shown in FIG. 2 has a concave solar reflective surface 10 that faces thesun 20 to reflect the solar energy to a focal point 21. In the followingdiscussion, the first major surface or outer surface 14 of the substrate12, and the concave surface 10 or outer surface 10 of the solar mirror 9are designated to face the incident radiation, e.g. the sun 20 (the sun20 shown only in FIG. 2), and the second surface 16 of the substrate 12and the convex surface 11 of the solar minor 9 faces an oppositedirection of the incident radiation. With continued reference to FIG. 1,the surface 16 of the substrate 12 is designated to support solarreflective coating 22 of the prior art as shown in FIG. 1. Optionally anunderlayer 24 is provided between the reflective coating 22 and thesurface 16 of the ply 12. A protective coating 25 discussed in detailbelow is applied over the solar reflective coating 22.

The solar mirror 7 of the invention shown in FIG. 3 includes thesubstrate or ply 12 with the first major surface 14, i.e. an outer majorsurface, and the opposed second major surface 16, i.e. an inner majorsurface. Solar reflective coating 27 of the invention is applied oversurface 29 of the underlayer 24 when an underlayer is present and overthe surface 16 of the substrate 12 when a underlayer is not present, andthe protective coating 25 applied over the solar reflective coating 27.In the following discussion, the first major surface 14 of the solarmirror 7 is designed to face the incident radiation, e.g. the sun, andthe second surface 16 of the substrate 12 faces in the oppositedirection of the incident radiation and is designated to support solarreflective coating 27 of the invention, Wit continued reference to FIG.3, solar mirror 7 of the invention includes a solar reflective coating27 having two sublayers 28 a and 28 b separated by a parting layer 30.Shown in FIG. 4 is a solar mirror 26 of the invention including threesublayers, e.g. sublayers 28 a, 28 b and 28 c separated by a partingfilm or medium 30 a and 30 b to reduce crystal growth. The solarreflecting coating 27 of the invention is discussed in more detailbelow.

In the broad practice of the invention, the substrate or ply 12 caninclude any desired material having any desired characteristics. Forexample, when the first major surface 14 of the ply 12 faces theincident radiation, e.g. sun 20 (the sun 20 shown only in FIG. 3) andthe second major surface 16 of the substrate or ply 12 supports orcarries sublayers 28 and parting layers 30 of the solar reflectivecoating, for example but not limited to sublayers 28 a and 28 b. The ply12 is preferably transparent or translucent to visible By “transparent”is meant having a transmission of greater than 0% up to 100% in adesired wavelength range, such as visible light. Alternatively, the ply12 can be translucent. “Translucent” is meant allowing electromagneticradiation (e.g., visible light) to be transmitted but diffusing orscattering this radiation. Examples of suitable materials for the ply 12include, but are not limited to, thermoplastic, thermoset, orelastomeric polymeric materials, glasses, ceramics, and metals or metalalloys, and combinations, composites, or mixtures thereof. Specificexamples of suitable materials include, but are not limited to, plasticsubstrates (such as acrylic polymers, such as polyacryrates;polyalkylmethacrylates, such as polymethylmethacrylates,polyethylmethacrylates, polypropylmethacrylates, and the like;polyurethanes; polycarbonates; polyalkylterephthalates, such aspolyethyleneterephthalate (PET), polwmpyleneterephthalates,polybutyleneterephthalates, and the like; polysiloxane-containingpolymers; or copolymers of any monomers for preparing these, or anymixtures thereof); ceramic substrates; glass substrates; or mixtures orcombinations of any of the above. For example, the ply 12 can includeconventional soda-lime-silicate glass, borosilicate glass, or leadedglass. The glass can be clear glass. By “clear glass” is meantnon-tinted or non-colored glass. Alternatively, the glass can be opaque,tinted or otherwise colored glass. The glass can be annealed orheat-treated glass. As used herein, the term “heat treated” meansthermally tempered, thermally bent, heat strengthened, or laminated. Theglass can be of any type, such as conventional float glass, and can beof any composition having any optical properties, e.g., any value ofvisible transmission, ultraviolet transmission, infrared transmission,and/or total solar energy transmission. Although not limiting to theinvention, examples of glass suitable for the substrate or ply 12 aredescribed U.S. Pat. Nos. 4,745,347; 4,792,536; 5,030,593; 5,030,594;5,240,886; 5,385872; and 5,393,593. The substrate or ply 12 can be ofany desired dimensions, e.g., length, width, shape, or thickness. In oneexemplary embodiment, the first ply 12 can be greater than 0 up to 25 mm(1.00 inch) thick, such as 1 mm to 10 mm thick, e.g., 1 mm to 6 mmthick, e.g., less than 4 mm thick, e.g., 3 mm to 3.5 mm thick, e.g., 3.2mm thick. Additionally, the ply 12 can be of any desired shape, such asfiat, curved, parabolic-shaped, or the like. Also, when the primaryreflective coating(s), e.g. the reflective coating 27 reside on thesecond major surface 16 of the solar mirror, the ply 12 can include, butis not limited to, one or more materials that exhibit low absorption ofelectromagnetic radiation in the region(s) of electromagnetic radiationdesired to be reflected.

In one non-limiting embodiment of the invention, the ply 12 can have ahigh visible light transmission at. a reference wavelength of 550nanometers (nm) and a reference thickness of 3.2 mm. By “high visiblelight transmission” is meant visible light transmission at 550 nm ofgreater than or equal to 85%, such as greater than or equal to 87%, suchas greater than or equal to 90%, such as greater than or equal to 91%,such as greater than or equal to 92%, such as greater than or equal to93%, such as greater than or equal to 96%, at 3.2 mm reference thicknessfor the ply. Particularly useful glass for the practice of the inventionis disclosed in U.S. Pat. Nos. 5,030,593 and 5,030,584. Non-limitingexamples of glass that can be used for the practice of the inventioninclude, but are not limited to, Starphire™, Solarphire™, Solatphire™,PV, Solargreen™, Solextra™, GL-20™, GL-35™, Solarbronze™, CLEAR, andSolargray™ glass, ell commercially available from PPG industries Inc. ofPittsburgh, Pa.

As can be appreciated by one skilled in the art, the ply 12 (see FIGS. 1and 3) is transparent when the ply 12 is between the sun 20 and thereflective coating 22, and the ply can be opaque or transparent when thesolar reflective coating is between the sun 20 and the ply.

With reference to FIG. 3, in another non-limited embodiment of theinvention, the layer 24 or undercoat 24 or underlayer 24 is providedbetween the sublayer 28 b of the so/air reflective coating 18 and thesecond major surface 16 of the ply 12. The undercoat 24 is preferablydeposited using a vacuum-based process and immediately prior todeposition of the vacuum-deposited silver (Ag) reflective coating layer27 without breaking vacuum so as to provide a virgin surface to receivethe solar reflecting coating 27. The undercoat 24 can provide a strongeror more durable interface between the ply 12 and the reflective coating27. The undercoat 24 can include, but is not limited to one or morematerials chosen such that the interface between the undercoat 24 andthe solar reflective coating 27 is more mechanically, chemically, and/orenvironmentally stable than an interface between the ply 12 and theprimary reflective coating 27. Also, the undercoat 24 can serve as adiffusion barrier to the elemental exchange between the ply 12 and thereflective coating 27 (such as the migration of sodium out of the glassply 12 into the overlying coating(s) or the migration of metal, e.g.,silver, from the reflective coating 27 to the glass), especially asmight occur as the result of subjecting the coated article to elevatedtemperatures, for example, for bending or heat strengthening.

Additionally or alternatively, the undercoat 24 can provide a smootheror more planar surface upon which to deposit an overlaying coating,e.g., the solar reflective coating 27. Examples of materials suitablefor the undercoat 24 include, but are not limited to, inorganicmaterials such as but not limited to light transmitting log absorptiondielectrics, such as metal oxides, metal nitrides and/or combinationsthereof, composites, or mixtures of metal oxides and/or metal nitrides,Examples of suitable metal oxides include alumina, silica, Mania,zirconia, zinc oxide, zinc stannate, tin oxide, or mixtures orcombinations thereof. Other examples for the underlayer 24 include oneor more layers of silicon dioxide and/or silicon nitride or combinationsthereof. In one non-limiting embodiment, the undercoat or underlayer 24includes but is not limited to titanic. The undercoat 24 can have anycomposition or thickness to provide sufficient functionality to thearticle (e.g., mechanical, chemical, passivation, planarization,adhesion, diffusion barrier properties, environmental durabilityenhancement, optical enhancement). In one particular embodiment wherethe undercoat 24 is titanic, the undercoat 24 has a thickness in therange of 0.1 nm to 5 nm, such as 0.1 nm to 3 nm, such as 0.5 nm to 3 nm,such as 1 nm to 3 nm, such as 0.6 nm to 2 nm, such as 1 nm to 2 nm, suchas 1.5 cm to 2 nm, such as 1.8 nm.

With reference to FIGS. 3 and 4 as needed, in the preferred practice ofthe invention, the sublayer 28 b of the solar reflecting coating 27 ofthe solar mirror 7 (FIG. 3). and the sublayer 28 c of the solarreflecting coating 27 of the solar mirror 26 (FIG. 4) are formed over atleast a portion of the second major surface 16 of the substrate 12, e.g.over at least a portion of the underlayer 24, if present, Optionally aprotective coating 25 is provided over at least a portion of the solarreflective coating 27. While in the illustrated embodiment shown inFIGS. 3 and 4, the underlayer 24, the solar reflective coating 27 andthe protective coating 25 are formed over the second major surface 16 ofthe substrate 12, it is understood that at least some of the coatingscould alternatively be formed over the first major surface 14 of thesubstrate 12. The selection of material of the solar mirrors 7 and 26 ofthe invention, e.g. but not limited to the materials of the substrate12, the optional undercoat or underlayer 24 employed to, among otherthings, act as a barrier coating to the solar reflective coating 27, andthe protective coating 25 is also discussed in U.S. Pat. No. 8,445,098(“Pat '098”) is hereby incorporated by reference, and no furtherdiscussion is deemed necessary.

For ease of referencing the coating or films, the coating or films arediscussed as individual coatings and films, e.g. but not limiting to theinvention, the individual films of the solar mirror 7 of the inventionshown in FIG. 3 are the underlayer 24, the solar reflective coating 27,which include sublayers 28 a and 28 b and the parting film 30, and theprotective film 26 as shown in FIG. 3. The individual films of the solarmirror 26 of the invention shown in FIG. 4 are the underlayer 24, thereflective coating 27, which include sublayers 28 a-c and the partingfilms 30 a-b, and the protective film 25 as shown in FIG. 4. Optionally,the films of the solar mirror 26 shown in FIG. 4 can collectively bereferred to as coating stack 34. For the prior art solar mirror 5 shownin FIG. 1 the individual films of the prior art solar mirror 5 shown inFIG. 1 are the underlayer 24, the solar reflective coating 22, and theprotective film 25 as shown in FIG. 1 can optionally be referred to asprior art coating stack 35.

With reference back to FIGS. 3 and 4 as needed, the solar reflectivecoating 27 is formed over at least a portion of the second major surface16, e.g., over at least a portion of the undercoat 24, if present. Thesolar reflective coating 27 of the invention includes, but is notlimited to, two or more sublayers 28, e.g. sublayers 28 a and 28 b inFIG. 3 and sublayers 28 a-c in FIG. 4. The component sublayers 28, inthe preferred practice of the invention are solar reflective material ormaterials that reflect portions of the electromagnetic spectrum. In onenon-limiting embodiment of the invention, the solar reflective coating28 includes, but is not limited to radiation reflective metallicsublayers 28 a and 28 b, or 28 a and 28 b and 28 c, and so forth.Examples of suitable reflective metals for the sublayers 28 of the solarreflective coating 27 include, but are not limited to, metallic silver,aluminum, gold, copper, platinum, iridium, osmium, palladium, ruthenium,rhodium, or other noble metals and alloys, mixtures, blends, orcombinations thereof. In one non-limiting embodiment of the invention,the solar reflective coating 27 includes, but is not limited to metallicsilver sublayers 28 such that thickness of the solar reflective coating27 has a thickness in the range of 50 nm to 500 nm, and preferable 100nm. The reflective solar coating 27 of FIG. 4 can be deposited to athickness such that the solar mirror 7 and 26 have any particulardesired level of reflectance in the desired range of electromagneticradiation to he reflected. The sublayers 28 a, 28 b and 28 c of thesolar reflective coating 27 can be deposited to a thickness sufficientthat the solar reflective coating 27 is opaque in a desired wavelengthrange, such as visible light. The solar reflective coating 27 can beparticularly useful in reflecting visible and solar infrared energy, inone particular non-limiting embodiment of the invention, the solarreflective coating 27 is deposited by a conventional sputtering process,as described in more detail below. In another non-limiting embodiment ofthe invention, the coating stack 32 of the solar mirror 7 can include,but is not limited to a “high reflector” having a plurality ofalternating high and low refractive index materials films as is known inthe art, e.g. see FIG. 11 and the discussion of FIG. 11 for additionalfilms.

The protective coating 25 assists in protecting the underlying layers ofthe coatings and/or films of the mating stack 32 of the solar mirror 7,and the coating stack 34 of the solar mirror 26 shown in FIGS. 3 and 4,respectively, from mechanical and chemical attack during manufacture,storage, transit, handling, processing, and/or during the mirror'sservice life in the field. The protective coating 25 also helps protectthe underlying layers from the ingress of liquid water, water vapor, andother environmental solid, liquid or gas pollutants. The protectivecoating 25 can be an oxygen barrier waiting layer to prevent or reducethe passage of ambient oxygen into the underlying layers duringsubsequent processing, e.g., such as during heating or bending. Theprotective coating 25 can be of any desired material or mixture ofmaterials, such as but not limited to one or more inorganic materials,in one exemplary embodiment, the protective coating 25 can include alayer having one or more metal oxide materials, such as but not limitedto oxides of aluminum, silicon, or alloys, blends, combinations, ormixtures thereof. For example, the protective coating 25 can be a singlecoating layer comprising an oxide deposited by sputtering a sputteringtarget comprising silicon and aluminum in the range of 0 wt. % to 100wt. % aluminum and/or 100 wt. % 0 wt. % silicon, such as 1 wt. % to 99wt. % aluminum and 99 wt. % to 1 wt. % silicon, such as 5 wt. % to 95wt. % aluminum and 95 wt. % to 5 wt % silicon, such as 10 wt. % to 90wt. % aluminum and 90 wt. % to 10 wt. % silicon, such as 15 wt. % to 90wt. % aluminum and 85 wt. % to 10 wt. % silicon, such as 50 wt. % to 75wt. % aluminum and 50 wt. % to 25 wt. % silicon, such as 50 wt. % to 70wt. % aluminum and 50 wt. % to 30 wt. % silicon, such as 35 wt. % to 100wt. % aluminum and 65 wt. % to 0 wt. % silicon, e.g., 70 wt. % to 90 wt.% aluminum and 30 wt. % to 10 wt. % silicon, e.g., 75 wt. % to 85 wt. %aluminum and 25 wt. % to 15 wt. % of silicon, e.g., 88 wt. % aluminumand 12 wt. % silicon, e.g., 65 wt. % to 75 wt. % aluminum and 35 wt. %to 25 wt % silicon, e.g., 70 wt. % aluminum and 30 wt. % silicon, e.g.,60 wt. % to less than 75 wt. % aluminum and greater than 25 wt. % to 40wt. % silicon. In one particular non-limiting embodiment, the protectivecoating 23 comprises an oxide deposited by sputtering a sputteringtarget comprising includes 40 wt. % to 15 wt. % aluminum and 60 wt. % to85 wt. % silicon such as 85 wt. % silicon and 15 wt. % aluminum. Othermaterials, such as aluminum, chromium, hafnium, yttrium, nickel, boron,phosphorous, titanium, zirconium, and or oxides thereof, can also bepresent, such as to adjust the refractive index of the protectivecoating 25. In one non-limiting embodiment, the refractive index of theprotective coating 25 can be in the range of 1 to 3, such as 1 to 2,such as 1.4 to 2, such es 1.4 to 1.8.

In one non-limiting embodiment of the invention the protective coating25 includes, but is not limited to a combination of silica and alumina.he protective coating 25 can be sputtered from two cathodes (e.g., onesilicon and one aluminum) or from a single cathode containing bothsilicon and aluminum. This silicon aluminum oxide protective coating 25can be written as Si.sub.xAl.sub.1-x.O.sub.1.5+x/2, where x can varyfrom greater than 0 to less than 1. In one specific non-limitingembodiment of the invention, the protective coating 25 can be a siliconaluminum oxide coating (Si.sub.xAl.sub.1-x.O.sub.1.5+x/2) having athickness in the range of 5 nm to 5,000 nm, such as 5 nm to 1,000 nm,such as 10 nm to 100 nm, e.g., 10 nm to 50 nm, such as 10 nm to 40 nm,such as 20 nm to 30 nm, such as 25 nm. Further, the protective coating25 can be of non-uniform thickness. By “non-uniform thickness” is meantthat the thickness of the protective coating 25 can vary over a givenunit area, e.g., the protective coating 25 can have high and low spotsor areas. In another non-limiting embodiment, the protective coating 25includes but is not limited to a silicon aluminum oxide coating ormixture, combination, alloy, or blend of silica and alumina, such as 85wt. % silica and 15 wt. % alumina, and has a thickness in the range of10 nm to 500 nm, such as 20 nm to 300 nm, such as 50 nm to 300 nm, e.g.,50 nm to 200 nm, such as 50 nm to 150 nm, such as 50 nm to 120 nm, suchas 75 nm to 120 nm such as 75 nm to 100 nm. In a particular non-limitingembodiment, the protective coating 25 can have a thickness of at least50 nm, such as at least 75 nm, such as at least 100 nm, such as at least110 nm, such as at least 120 nm, such as at least 150 nm, such as atleast 200 nm.

In another non-limiting embodiment of the invention, the protectivecoating 25 includes but is not limited to silica having a thickness inthe range of 10 nm to 100 nm, such as 10 nm to 80 nm, such as 20 nm to80 rim, such as 30 nm to 70 om, such as 40 nm to 00 nm, such as 50 nm.In a further non -limiting embodiment, the protective coating 25includes, but is not limited to, silica having a thickness in the rangeof 10 nm to 500 nm, such as 10 nm to 400 nm, such as 20 nm to 300 nm,such as 50 nm to 200 nm, such as 75 nm to 150 nm, such as 75 nm to 120nm.

In another non-limiting embodiment of the invention, the protectivecoating 25 can include a multi-layer structure, e.g., a first layer withat least one second layer formed over the first layer. In one specificnon-limiting embodiment, the first layer can include, but is not limitedto alumina or a mixture, combination, blend, or alloy including aluminaand silica. For example, the first layer can include, but is not limitedto a silicon aluminum oxide deposited by sputtering a sputtering targethaving greater than 5 wt. % aluminum, such as greater than 10 wt. %aluminum, such as greater than 15 wt. % aluminum, such as greater than30 wt. % aluminum, such as greater than 40 wt. % aluminum, such as 50wt. % to 60 wt. % aluminum, such as in the range of 70 wt. % to 100 wt.% aluminum and 40 wt. % to 0 wt. % silicon, such as greater than 90 wt.% aluminum, such as greater than 96 wt. % aluminum. In one non-limitingembodiment, the first layer includes all or substantially all aluminumoxide. In one non-limiting embodiment, the first layer can have athickness in the range of greater than 0 nm to 1 micron, such as 5 nm to10 nm, such as 10 nm to 25 nm, such as 10 nm to 15 nm. The second layercan comprise silica or a mixture, combination, blend, or alloycomprising silica and alumina. For example, the second layer cancomprise a silicon aluminum oxide deposited by sputtering a sputteringtarget having greater than 40 wt. % silicon, such as greater than 50 wt.% silicon, such as greater than 60 wt. % silicon, such as greater than70 wt. % silicon, such as greater than 80 wt. % silicon, such as in therange of 80 wt. % to 90 wt. % silicon and 10 wt. % to 20 wt. % aluminum,e.g., 85 wt. % silicon and 15 wt. % aluminum. In one non-limitingembodiment, the second layer can have a thickness in the range ofgreater than 0 nm to 2 microns, such as S rim to 500 nm, such as 6 nm to200 nm, such as 10 nm to 100 nm, such as 30 nm to 50 nm, such as 35 nmto 40 nm. In another non limiting embodiment, the second layer can havea thickness in the range of greater than 0 nm to 1 micron, such as 5 nmto 10 nm, such as 10 nm to 25 nm, such as 10 nm to 15 nm. In anothernon-limiting embodiment, the protective coating can be a bilayer formedby one metal oxide-containing layer (e.g., a silica and/oralumina-containing first layer) formed over another metaloxide-containing layer (e.g., a silica and/or alumina-containing secondlayer) wherein the two components of said bilayer protective coatinghave different chemical compositions. The individual layers of themulti-layer protective coating 25 can be of any desired thickness.Non-limiting examples of suitable protective coatings 25 are described,for example, in U.S, patent application Ser. Nos. 10/007,382;10/133,805; 10/397,001; 10/422,094; 10/422,095; and 10/422,096, whichdocuments are incorporated herein by reference.

Comparing the solar mirrors 7 and 26 of the invention shown in FIGS. 3and 4, respectively to the prior art solar mirror 5 shown in FIG. 1, thedifference of interest to the present discussion is the solar reflectingcoating 22 of the prior art solar mirror 5, and the solar reflectingcoating 27 of the solar mirrors 7 and 26 of the invention. Moreparticularly, the substrate 12, the underlayer 24 and the protectivecoating 25 of the prior art solar mirror 5 shown in FIG. 1, and of thesolar mirrors 7 and 26 shown in FIGS. 3 and 4 respectively are similarif not identical. Based on the forgoing it can be appreciated that thedifference between the solar mirrors of the prior art and the solarmirrors of the invention is the solar reflecting waling. Moreparticularly, the solar reflecting coating 22 of the prior art is amonolithic solar reflecting film 22, e.g. a single silver (Ag) filmwhereas the solar reflecting coating 27 of the invention includes solarreflecting films or sublayers 28 separated by parting layers 30.

In the following discussion, reference is made to the non-limitingembodiment of the solar reflective coating 27 of the solar mirror 7 ofthe invention (see FIG. 3). The discussion, however, unless indicatedotherwise is also applicable to the non-limiting embodiment of the solarreflective coating 27 of the solar mirror 26 of the invention (see FIG.4). With reference to FIGS. 3 and 4 as needed, the solar reflectivecoating 27 of the invention has the parting layer 30 between thesublayers 28 a and 28 b (see FIGS. 1 and 3), and has the parting layers30 a and 30 b between the sublayers 28 a, 28 b and 28 c (FIG. 4). Withreference to FIG. 4, surface 38 of the parting layer 30 a can be insurface contact with adjacent surface 40 of the sublayers 28 a or 28 band 28 c if present, or a coating or film can be provided between thesurface 35 of the parting layer 30 and the surface 40 of the sublayers28 a and 28 b. Without limiting the scope of the invention, thenon-limiting embodiment of the invention can be considered a solarmirror 7 having a solar reflective coating 27 having two solarreflective sublayers 28 a and 28 b (FIG. 3) and 28 c (see FIG. 4separated by a parting layer 30 a (FIG. 3) and 30 b (FIG. 4). in thepractice of the invention, the surface 40 of the sublayer 28 a is insurface contact with, or over adjacent surface 38 of the parting layer30, and surface 40 of the sublayer 28 b is in surface contact with thesurface 38 of the parting layer 30. Notwithstanding the forgoing, theinvention contemplates having additional eating layers between thesurfaces 40 of the sub layers 28 a and 28 b, respectively of the solarreflective coating 27, and surfaces 38 of the parting film 30 a and 30b, as shown in FIG. 4. This non-limiting embodiment of the invention isdiscussed in more detail below.

Practicing the invention provides a solar mirror 7 and 26 that Isoptically more stable at elevated temperatures, e.g. 1180 to 1200° F., atemperature range that is suitable for high-temperature heat-treatmentof glass such as thermal tempering, heat-strengthening, or bending, ofthe glass. Further, the solar reflectance coating 27 can exhibit a rangeof solar reflectance or transmittance in the region(s) of interestwithin the electromagnetic spectrum (e.g., ultraviolet, visible, nearinfrared, far infrared, microwave, radiowave, etc.). For example but notlimiting to the invention, the solar mirrors 7 and 26 (FIGS. 3 and 4,respectively) can have a visible light reflection at a wavelength of 550nm of at least 85%, such as at least 90%, such as at least 95% of the“visible light” reflectance adjacent one or more silver sublayers 28 a,28 b, (FIG. 3) and 28 c (FIG. 4).

The practice of the invention mitigates a potential reduction in thespecular reflectance of the solar mirror of the invention, e.g. but notlimited to solar mirrors 7 and 26 of FIGS. 3 and 4, respectively, byreducing the amount of light that is non-specularly (i.e. diffusely)reflected from the solar mirror 7 and 26 of the invention.

In order to illustrate the benefits of the instant invention, a term“specular-included reflectance” was adopted to mean all specular andnon-specular (i.e. diffuse) contributions to the mirror's reflectance.Typically, one seeks to minimize the amount of specular-excluded (i.e.diffuse) reflectance in order to maximize the mirror's specularreflectance. A commercially available spectrophotometer can be used tomeasure the specular-included reflectance (which includes both specularand non-specular components) and its specular-excluded component. Theinstrument used to do so was a Hunter Ultrascan PRO spectrophotometer.The measured wavelength range was 350-1000 nm. The glass-side (i.e,energy incident on the uncoated surface of the specimen)specular-Included reflectance measured by the instrument is tabulated asa percentage of the incident light that is specularly and non-specularlyreflected versus wavelength. Similarly, the glass-side specular-excludedreflectance measured by the instrument is tabulated as a percentage ofthe incident light that is non-specularly reflected versus wavelength.The tabulated values of specular-excluded reflectance can be weighted bythe solar irradiance function and numerically integrated to yield asingle number which we refer to as “specular-excluded solar-weightedglass-side reflectance” (often abbreviated herein as “SpEx WIRg” where“WIR” means “(solar-)weighted integrated reflectance”, “Sp Ex” mean“specular-excluded”, and the “g” subscript indicates that the lightenergy is incident on the glass-side (i.e. uncoated surface) of thesolar mirror 7. For solar mirror applications, the surface(s) that areintended to receive the flux of reflected sunlight is/are referred to asthe “receiver”. It is typically desirable to minimize thespecular-excluded solar-weighted glass-side reflectance (SpEx WIRg)because any light energy that is non-specularly reflected from a solarmirror may not be intercepted by the receiver's surface, therebyconstituting a loss of the available incident solar energy.

Two samples for comparison were made. Sample 1 was a prior art solarmirror designated by the number 70 and shown in FIG. 5, and Sample 2 wasa non-limiting embodiment of a solar mirror of the invention designatedby the number 72 and shown in FIG. 6. With reference to FIG. 5, thesolar mirror 70 (Sample 1) of the prior art included:

-   -   1. A low iron glass substrate 12 of the type sold by PPG        Industries Inc. under the registered trademark SOLARHIRE PV had        a nominal thickness of 3.2 millimeter (“mm”);    -   2. A titania (TiO2) undercoat or underlayer 74 had a thickness        of 2 nm applied by MSVD to the surface 16 of the glass substrate        12;    -   3. A solar reflective coating of silver (“Ag”) 22 had a        thickness or 100 nm was applied by MSVD on the TiO2 undercoat        film 74;    -   4. A Ti(Ox) “primer” or “barrier” or “blocking” layer 76 had a        thickness of 2.5 nm applied by MSVD on the Ag film 22;    -   5. An oxide film of 52 wt. %-48 wt. % Sn (“Zn 52-Sn48 oxide”)        topcoat layer 78 had a thickness of 140 nm; also referred to as        zinc stannate (Zn2SnO4) a piled by MSVD on the Tl(Ox) “primer”        layer 76;    -   6. An oxide of 85 wt. %. Si-15 wt. % Al (“Si85-Al15”)        aluminosilicate film 25, the film also known as Permanent        Protective Overcoat (“PPO”) had a thickness of 75 nm was applied        on the “Zn52-Sn48 oxide” film 78; the (“Si85-Al15”)        aluminosilicate film 80 applied on the “Zn52-Sn48” topcoat layer        film 78.

With reference to FIG. 6, the solar mirror 72 of the invention (Sample2) included but is not limited to:

-   -   1. A low iron glass substrate 12 of the type sold by PPG        Industries under the registered trademark SOLARPHIRE PV had a        nominal thickness of 3.2 millimeter (“mm”);    -   2. A titania (TiO2) undercoat film 74 had a thickness of 2        nanometer applied by MSVD to the surface 16 of the glass        substrate 12;    -   3. A sublayer 28 b of a silver (“Ag”) film 27 had a thickness of        50 nm applied on the TiO2 film 74;    -   4. A Ti(Ox) first parting film 82 had a thickness of 1.3 nm        applied on the sublayer 28 b of the Ag (50 nm) film;    -   5. A Zn2SnO4 second parting film 84 had a thickness of 3.6 nm on        the patting Ti(Ox) film 82;    -   6. A silver sublayer 28 a of the silver (“Ag”) coating had a        thickness of 50 nanometers (“nm”) applied on the Zn2SnO4 second        parting film 84;    -   7. A Ti(Ox) “primer” or “barrier” or “blocker” layer 76 had a        thickness of 2.5 nm on the Ag sublayer 28 a;    -   8. An oxide film of 52 wt. % Zn-48 wt. % Sn (“Zn52-Sn48 oxide”)        topcoat layer 84 had a thickness of 140 nm; also referred to as        zinc stannate (Zn2SnO4) applied by MSVD on the Ti(Ox) “primer”        layer 76;    -   9. An oxide of 85 wt. % Si-15 wt. % Al (“Si85-Al15 oxide”)        aluminosilicate film (the PPO film) 25 having a thickness of 75        nm was applied on the “Zn52-Sn48” oxide film.

The Ti(Ox) film 76 for solar mirrors 70 and 72 did not have a sub numberbecause the titanium (Ti) is deposited as metallic titanium inside thevacuum system and reacts with oxygen as the coating process continues.After coating deposition is complete, the titanium (Ti) has eithercompletely oxidized or nearly completely oxidized. It the titanium isnot completely oxidized in the as deposited state, any residual TiO_(x)metallic titanium is expected to fully oxidized by subsequenthigh-temperature thermal processing (e.g. thermal tempering,heat-strengthening, bending).

FIG. 7 is a graph showing approximate specular-excluded solar-weightedRg reflectance (“SpEx WIRg”), estimated using 350-1000 nm spectral Rreflectance data, of experimental solar mirror coatings with and withoutsolar reflecting coating 27 of the invention having parting layers 82and 84, and sublayers 28 a and 28 b. As can be appreciated from theabove discussion, the coating stack 86 of the solar mirror 70 of theprior art, and coating stack 88 of the solar mirror 72 of the inventionare nominally identical except the prior art solar mirror 70 employs amonolithic Ag film 22, and the solar reflecting mirror 72 of theinvention has the parting layers 82 and 84 in the mating stack 88 of thesolar mirror 72 of the invention. The left side of the plot shows thespecular-excluded solar-weighted glass-side reflectance of both solarmirrors 70 and 72 in their as-deposited/non-heat-treated state. Theright side of the plot shows the specular-excluded solar-weightedglass-side reflectance of both solar mirrors 70 and 72 after heattreatment to simulate thermal tempering. Considering the left side ofthe plot, the column at the extreme left is the data for solar mirror 70without the parting films 82 and 84 of the invention, and the columnimmediately adjacent to the right is the data for solar mirror 72 of theinvention with the parting films 82 and 84 of the invention. As one cansee from FIG. 7, in their as-deposited/non-heat-treated states, thespecular-excluded solar-weighted glass-side reflectance of solar minors70 and 72 is similar. Considering the right side of the pot of FIG. 7,the column at the extreme, right is the date for the solar mirror 72with the parting films 82 and 84 of the invention; the columnimmediately adjacent to the left is the data for solar mirror 70 withoutthe parting films 82 and 84 of the invention. As one can see from FIG.8, after heat-treatment to simulate thermal tempering, thespecular-excluded solar-weighted glass-side reflectance of solar mirror72 is: (a) similar to the value of the SpEx WIRg of the Solar mirror 72in its as-deposited state, and (b) is lower than that of solar mirror 70after solar mirror 70 has been subjected to heat-treatment. As is nowappreciated, it is typically desirable to minimize Spa WIRg for solarmirror applications.

The information of FIG. 7 demonstrates that the prior art solar mirrorand the solar mirror of the invention have about the same level ofspecular-excluded reflectance in their as deposited states, butsignificant differences when heat-treated. Specifically, in theas-deposited/non-heated state, the prior art coated substrate 12 (solarmirror 70) and the coated substrate 12 of the invention (solar mirror72) exhibited little/no haze, based on a qualitative visual assessmentwherein the solar mirrors 70 and 72 were viewed in reflectancer: underincandescent floodlight illumination.

Furthermore, the “truncated” (350-1000 nm) estimated (solar) weightedspecular-excluded reflectances, SpEx WIRg, of solar mirror 70 and solarmirror 72, in their as-deposited/non-heated states, were similar atabout 0.09-0.1%. After heat-treatment to simulate thermal tempering, thespecular-excluded solar-weighted Rg reflectance of the prior art solarmirror 70 exhibited about a three-fold increase to SpEx WIRg ˜0.33%,whereas the reflectance of the solar mirror 72 of the invention,exhibited only a slight increase to SpEx WIRg ˜0.13% (see FIG. 7).

Thus, FIG. 7 illustrates one benefit of the use of parting layers of theinvention—namely, the ability to suppress an increase inspecular-excluded solar-weighted Rg reflectance (“SpEx WIRg”)immediately after high-temperature heat-treatment. Herein we refer tothe Spa WIRg value measured immediately/shortly after high-temperaturethermal tempering heat-treatment, without significant additional agingat morn temperature or other temperatures, as the “time-zero SpEx WIRg”.Further sometimes the terms “haze”, “non-specularity”,“specular-excluded WIRg refelctance”, and “SpEx WIRg” are usedsynonymously.

Another feature of the solar reflective coating of the invention isimproved thermal stability of heat-treated mirrors aged at elevatedtemperatures, An experiment was conducted to simulate the performance ofthe solar mirror of the prior art (Sample 3), and a solar mirror of theinvention (Sample 4) for a period of time greater than 10,000 hours at atemperature of 150° C. With reference to FIG. 5, Sample 3 includes butsnot limited to:

-   -   1. The SOLARPHRE PV glass substrate 12 having a nominal        thickness of 3.2 mm;    -   2. The TiO2 film 74 having a thickness of 2 nm is applied on the        surface 16 of the substrate 12 facing away from the incident        light, e.g. but not limited to the sun 20 (see FIG. 2);    -   3. The silver (“Ag”) film 22 having a thickness of 100        nanometers (“nm”) applied on the film 74 of TiO2;    -   4. Inconel 600 corrosion-resistance-enhancing and UV-absorbing        film 90 having a thickness of (30 nm) is applied on the Ag        silver film 22. The Inconel 600 is shown in phantom and only        shown in FIG. 5;    -   5. The Ti(Ox) “primer” (or “barrier” or “blacker”) layer 76        (˜2.5 nm) on the Inconel 600 layer 90;    -   6. The oxide film of 52 wt. % Zn-48 wt. % Sn (“Zn52-Sn48 oxide”)        topcoat layer 78 having a thickness of (140 nm) on the Ti(Ox)        “primer” 76; and    -   7. The Permanent Protective Overcoat layer 25 having a thickness        of (75 nm) on the (“Zn52-Sn48 oxide”) topcoat layer 78.

Sample 4 was a solar mirror of the invention and was similar to thesolar mirror 72 shown in FIG. More particularly Sample 4 had:

-   -   1. The SOLARPHIRE PV glass substrate 12 having a nominal        thickness 3.2 mm; 2, The TiO2 film 74 haying a thickness of 2 nm        on the major surface 16 of the substrate 12 facing away from the        incident light, e.g. but not limited to the sun 20 (see FIG. 3);    -   3. The first sliver (Ag) sublayer 28 b of a silver (Ag) solar        reflective coating 27 having a thickness of 50 nm on the TiO2        film 74;    -   4. A first Ti(Ox) parting film 82 had a thickness of about 1 nm        on the Ag sublayer 28 b having a thickness of 50 nm;    -   5. A second parting film comprising an oxide of 52 wt. % Zn-48        wt. % Sn (“Zn52-Sn48 oxide”) 84, also known as zinc stannate        (Zn2SnO4); the second parting oxide film 84 of Zn52-Sn48 having        a thickness of about 1 nm on the first Ti(Ox) parting film 82;    -   6. The second sublayer Ag film 28 a having a thickness of 50 nm        on the first Ti(Ox) parting film 82;    -   7. The Inconel 600 corrosion-resistance-enhancing and        UV-absorbing layer (not shown) having a thickness of 30 nm on        the second Ag sublayer 28 a);    -   8. Ti(Ox) “primer” (or “barrier” or “blocker”) layer 76 had a        thickness of ˜2.5 nm on the Inconel 600 layer 90;    -   9. The oxide film of 52 wt. Zn-48 wt. % Sn (“Zn52-Sn48 oxide”)        topcoat layer 78 had a thickness of 140 nm on the Ti(Ox)        “primer” 76; and    -   10. The Permanent Protective Overcoat (PPO) layer 25 had a        thickness of 75 nm on the Zn52-Sn48 oxide topcoat layer 78.

It is noted that Sample 4 had two parting films 82 and 84 between twolayers (see two parting films shown in FIG. 6) and the parting film 84is a titanium oxide or titanium sub-oxide film which functions similarto the Ti(Ox) film 70 of solar mirror 72 shown in FIG. 6. The thicknessof the parting layer is the sum of the thicknesses of all the partingfilms between the layers of the solar reflective coating, e.g. but notlimited to 28 a and 28 b. For example and not limiting to the inventionthe thickness of the parting layer between the layers 28 a and 28 b,which comprises the parting films 82 and 84, of Sample 4 is about 2 nm.

The use of the corrosion-resistance-enhancing and UV-absorbing layer,e.g. the Inconel 600 film 90 is not limiting to the invention and is anoptional feature of the invention. The corrosion-resistance-enhancingand UV-absorbing layer (hereinafter also referred to as the“corrosion-resistance-absorbing layer”) provides various benefits, suchas corrosion inhibition and ultraviolet screening benefits. Also, thecorrosion-resistance-absorbing layer can provide some amount ofelectromagnetic energy reflection, which can permit a thinner primaryreflective layer, e.g. but not limited to the sliver film. Thecorrosion-resistance-absorbing layer 90 can also provide mechanicaland/or chemical protection to the underlying coating layers. Thecorrosion-resistance-absorbing layer can be provided under, over, orbetween one or more coating layers, e.g., the solar reflectivecoating(s) 27 or the top coat 78 (described above). Examples of suitablematerials for the corrosion-resistance-absorbing layer include, but arenot limited to, elemental metals and alloys of two or more metallicelements which are members of Groups 2-16 of the Periodic Table of theElements, including, but not limited to, nickel and nickel-containingalloys ferrous alloys and iron-containing alloys such as stainlesssteels, aluminum end aluminum-containing alloys, copper andcopper-containing alloys, chromium and chromium-containing alloys,titanium and titanium-containing alloys, brasses such as Naval brass (analloy of Cu, Zn and Sn), Admiralty brass (an alloy of Zn, Sn and Cu),and Aluminum brass (an alloy of Cu, Zn and Al), cobalt andcobalt-containing alloys such as alloys of cobalt and chiomium, zinc andzinc-containing alloys, tin and tin-containing alloys, zirconium andzirconium-containing alloys, molybdenum and molybdenum-containingalloys, tungsten and tungsten-containing alloys, niobium andniobium-containing alloys, indium and indium-containing alloys, lead andlead-containing alloys, and bismuth and bismuth-containing alloys.Specific non-limiting embodiments include corrosion-resistant metals andmetal alloys including, but not limited to, nickel and nickel-containingalloys such as Nickel 200, Inconel alloys such as Inconel 600 andInconel 625, stainless steels such as stainless steel 304 and stainlesssteel 316. Monel® alloys such as Monel 400, Hastelloy® alloys, cobaltand cobalt-containing alloys such as Stellite® alloys, Inco alloys suchInco Alloy C-276 and Inca Alloy 020, Incol® alloys such as Incoloy 800and Incoloy 825, copper and copper-containing alloys such as brassesespecially Neval Brass (approximately 59% copper, 40% zinc, and 1% tin)and Admiralty Brass (approximately 69% copper, 30% zinc, 1% tin),silicon and silicon-containing alloys, titanium and titanium-containingalloys, and aluminum and aluminum-containing alloys such as aluminum6061. If present, the anti-corrosion coating(s) 90 can have any desiredthickness. In some non-limiting embodiments, thecorrosion-resistance-absorbing layer can have thicknesses in the rangeof, but not limited to, 1 nm to 500 nm, such as 1 nm to 400 nm, such as1 nm to 300 nm, such as 1 nm to 200 nm, such as 1 nm to 100 nm, such as10 nm to 100 nm, such as 20 nm to 100 nm, such as 30 nm to 100 nm, suchas 40 nm to 100 nm, such as 50 nm to 100 nm, such as 20 nm to 40 nm,such as 30 nm to 40 nm, such as 30 nm to 35 nm.

Corrosion-resistance-absorbing layers are well known in the art and nofurther discussion is deemed necessary. For a more detailed discussionof corrosion-resistance-absorbing layer reference can be made to column9, line 45 to column 11, line 2 of U.S. Pat. No. 8,445,098, which patentin its entirety is incorporated herein by reference.

FIG. 8 is a graph showing approximate specular-excluded solar-weightedRg reflectance (SpEx WIRg) of Samples 3a and 4e with their coating inthe as deposited, unheated condition, and of Samples 3b and 4b withtheir coating in the deposited heated condition, i.e. maintained at 150degrees C. (heated). For purposes of clarity Sample 3a is designed as aprior art solar mirror after heat-treatment at Time Zero to simulatethermal tempering (hereinafter referred to as “heated”); Sample 35 isdesigned as a prior art solar mirror in its as-deposited state (a.k.a.“unheated” and/or “as-deposited”); Sample 4a is designed as a solarmirror of the invention in its as-deposited state(“unheated/as-deposited”), and Sample 4b is designed as a solar mirrorof the invention after heat-treatment at Time Zero to simulate thermaltempering (also known as “heated”).

In their as-deposited (i.e. non-heat-treated) states, Sample 3a andSample 4a exhibit relatively low values of SpEx WIRg as a function ofaging time. In contrast, after heat treatment to simulate thermaltempering at Time Zero, Sample 3b (prior art) exhibits, a rapid increasein SpEx WIRg at relatively snort (e.g. 10-100 hours) aging times, and amore-gradual increase at longer aging times as shown by Curve 3b in FIG.8. In contrast, heat-treated Sample 4b exhibits lower SpEx WIRg than theheat-treated Sample 3b at aging times greater than about 10 hours, andonly a gradual increase with aging time thereby suggesting that theheat-treated Sample 4b is intrinsically more thermally stable thanheat-treated Sample 3b. Furthermore, note that the SpEx WIRg values ofheat-treated Sample 4b are similar to the SpEx WIRg values of Samples 3aand 4a in their as-deposited states throughout most of the aging of thespecimens at 150° C.

From the above discussion the benefits and limitations of the solarreflective coating 27 of the invention that includes two or more layers28 a and 28 b can now be appreciated. in the preferred practice of theinvention, the parting films 30 (FIG. 3) and 82 and 84 (FIG. 6) is lessthan 5% of the solar reflective film's thickness. The hypothesis is thatthe parting film is a material that prevents, or breaks up, the crystalgrowth of the silver; smaller silver crystallites are expected toscatter light lees strongly than larger silver crystallites. Thus,coatings having solar reflective coatings comprising smaller silvercrystallites are expected to exhibit lower haze and lower specularexcluded solar-weighted glass-side reflectance (SpEx WIRg) than coatingshaving solar reflective coatings comprising larger sliver crystallites.Materials that can be used for parting films can include, but are notlimited to, oxides of metals, e.g. but not limited to oxides of Ti, Sn,Zn and combinations thereof. However, if desired, metals such astitanium can be used as parting layers, but such metallic materials willfend to be absorptive and therefore reduce the overall level of solarreflectance.

In this embodiment of the invention, the solar reflective coating 27 canbe any material that reflects solar energy, such as but not limited togold, silver, aluminum, copper, platinum, osmium, iridium, ruthenium,rhodium, palladium, or other noble metals and combinations, alloys,mixtures, or, blends thereof. Solar reflecting coating 27 can have twofilms 28 a and 28 b of the same material, e.g. silver films 28 a and 28b, or of different material, e.g., film or sublayer 28 a of silver and28 b of gold. The solar reflecting layer can include two films havingthe same thickness, or two films having afferent thicknesses. Stillfurther, the solar reflecting coating 27 can have more than two films,e.g. the solar reflecting coating can include three, four, five or morefilms having one or more parting layers between adjacent solarreflecting films.

The invention is not limited to the thickness of the parting layer(s),however, in the practice at the invention, the parting layer 30 has athickness sufficient to inhibit thermally-activated crystal growth ofthe layers, e.g. but not limited to the layers 28 a and 28 b, such asmight occur while the coated article is in service either at ambienttemperatures or elevated temperatures. By way of illustration and notlimiting to the invention, the prior art solar reflective coating 22(see FIG. 1) is a silver coating having a thickness of 100 nm and couldcomprise silver crystallites having sizes ranging from greater than zeroup to the full thickness of the solar reflective layer 22 (100 nm inthis example) In contrast, the solar reflective coating 27 (see FIG. 3)of the invention has a solar reflective coating having two layers, e.g.but not limiting to the invention, silver layers 28 a and 28 b eachhaving a thickness 50 nm. Thus, the layer 28 a could comprise silvercrystallites ranging from greater than zero only up to the fullthickness of the silver layer 28 a (only 50 nm in this example).Similarly, the layer 28 b could comprise silver crystallites rangingfrom greater than zero only up to the full thickness of the silver layer28 b (only 50 nm in this example). The thickness of the parting film 30is selected to cooperate with the films, coating and layers of thecoating stack to provide the optical performance (e.g. spectralreflectance) of the solar mirror. In a non-limiting embodiment of theinvention the parting film 30 has a thickness in the range of greaterthan zero to 5 nm

Further, the invention is not limited to the optical properties at thesolar mirror, however, in the preferred practice of the invention, thesolar energy passes through the substrate 12, through the films of thecoating stack to reflect the solar energy from the solar reflecting film27 to a selected position to act on the reflected solar energy.

In one particular embodiment, the layers 28 a and 28 b of the reflectivecoating 27 are silver films each having a thickness in the range of 1 nmto 150 nm, such as 2 nm to 125 nm, such 25 nm to 150 nm, such as 50 nmto 100 nm, such as 100 nm to 200 nm, such as 100 nm to 150 nm, such as110 nm to 140 nm, such as 120 nm to 140 nm, such as 128 nm to 132 nm. Inanother particular embodiment, the reflective coating 27 includesmetallic silver having a thickness in the range of 1 nm to 500 nm suchas 50 nm to 500 nm, such 50 nm to 300 nm, such as 50 nm to 200 nm, suchas 50 nm to 150 nm, such as 70 nm to 150 nm, such as 90 nm to 120 nm,such as 90 nm to 130 nm, such as 90 cm to 100 nm, such as 90 nm to 95nm. In the preferred practice of the invention, the silver layers 28 aand 28 b have a thickness in the range of 25-75 nm preferable 40-60,e.g. 50 nm.

In one non-limiting embodiment of the invention, the thickness of thelayers 28 a and 28 b of the solar reflecting film 27 of FIG. 3, e.g. butnot limited to a silver film having the parting layer 30 is determinedby designing a solar mirror having a single solar reflecting film of thedesired design thickness as is presently done in the art. The calculatedthickness of the solar reflecting layer is divided by the number ofsolar reflecting films to be used, e.g. for two solar reflecting filmsthe thickness of the reflecting layer is divided by 2, for three solarreflecting films the thickness of the reflecting layer is divided by 3,and so on.

With continued reference to FIG. 3, the surface 16 of the substrate 12designated to face away from the sun 20 (see FIG. 2) is coated with theTiO₂ layer 24, the first sublayer 28 b of the silver reflecting coating27 is applied over the TiO₂ film 24 (FIG. 3), 74 (FIG. 6), the partingfilm 30 is applied over the layer 28 b of silver, the layer 28 a of thecoating 27 is applied over the parting layer 30 and the protectivecoating 25 is applied over the layer 28 a. As can be appreciated, theinvention is not limited to the coatings discussed herein and anycombination of coating, e.g. but not limited to the coatings of thesolar mirrors disclosed in Pat '098 can be used in the practice of theinvention.

The apparatus used to coat the substrate 12 is not limiting to theinvention and can include any of the types known in the art to applycoating and films to a substrate and to one another, such as but notlimited to MSVD and coating vapor deposition.

From the above discussion, the benefits and limitations of the solarreflective coating of the invention can now be appreciated. Moreparticularly, the parting film is a material that can be deposited overa layer of solar reflective coating to the growth of sliver crystallitescomprising the solar reflecting films, e.g. layers 28 a and 28 b, in thepractice of the invention, the thickness of the parting layer 30 is inthe range 0.005 to 10%, preferably in the range of 0.05 to 7.5%, morepreferably in the range of 0.5 to 5%, and most preferably in the rangeof 1.0 to 4% of the thickness of the solar reflective film 27, whichincludes the sublayers 28 a and 28 b. Materials that can be usedinclude, but are not limited to, oxides of metals, e.g. but not limitedto oxides of Ti, Sn, Zn and combinations thereof. However, if desired,metals, such as titanium can be used as parting film, but such metallicmaterials will tend to be absorptive of the solar energy passing throughsubstrate and coating stock. and therefore can reduce the overall levelof solar reflectance.

Encapsulated Coating Stack for a Solar Mirror to Increase Useable Lifeof the Solar Mirror

In the above discussion of solar mirrors, e.g. but not limited to solarmirrors (FIG. 1), 7 (FIG. 3), 26 (FIG. 4), 70 (FIG. 5), and 72 (FIG. 6)reference was made to the Permanent Protective Overcoat (“PPO”) 25. ThePPO protects the films of the coating stack 35, 32, 34, 86 and 88 (FIGS.1, 2, 4, 5 and 6, respectively) between the surface 16 of the substrate12 and the respective PPO layer of the coating stack 32. For example andnot limiting to the invention, the PPO coating 25 of the solar mirror 26of FIG. 4 protects surface 89 of the sublayer 28 a of the solarreflective coating 28 against chemical and mechanical damage duringhandling and transporting the solar mirrors.

Shown in FIGS. 9 and 10 are non-limited embodiments of solar mirrors 100and 102, respectively, of the invention having the PPO coating 25 andouter encapsulation 104 of the invention. In general, the solar mirror100 shown in FIG. 9 includes the coating stack 35 on the inner surface16 of the substrate 12, and the encapsulation 104 covering outer walls106 and top surface 108 of the coating stack 35. In general, the solarmirror 102 shown in FIG. 10 includes the coating stack 32 applied to theinner surface 16 of the substrate 12, and the encapsulation 104 coveringouter walls 110 and top surface 112 of the costing stack 32.

As is appreciated L by those skilled in the art, solar-reflectivecoatings, especially those which employ saver layer(s) are susceptibleto mechanical damage and/or environmental degradation/corrosion in theenvironment in which the solar mirrors are used, e.g. used in theoutdoor environment. In the practice of the invention, the encapsulantfor a second surface solar mirror is transparent because the source ofsoar energy faces the surface 16 of the substrate 12, whereas a firstsurface solar reflecting solar mirror has the surface 14 of thesubstrate facing the source of solar energy. Stated another way,encapsulants 104 covering the coating stacks 32 and 35 of first surfacemirrors are transparent because the encapsulant 104 is within theoptical path of the incident and reflected light. Encapsulants 104covering the coating stacks 32 and 35 of second surface mirrors areopaque because the encapsulant 104 is not within the optical path of theincident and reflected light. The primary durability screening test forsolar minors having an encapsulant over the coating stack is generallyaccepted to be the Copper Accelerated Acetic Acid Salt Spray (“CASS”).The CASS test is well known in the art and further discussion regardingthe CASS test is not deemed necessary.

In addition to encapsulant failing the CASS test, another drawback withthe presently available encapsulants is the use of a lead (“Pb”)basedcorrosion inhibitor in order to sufficiently protect the underlyingAg-based reflective coating from corrosion/degradation and loss ofreflectance. In the years since such “high-Pb” encapsulants weredeployed, the burgeoning concentrated solar power (CSP) industry hasfavored encapsulants having decreasing amounts of Pb, and preferablyessentially being free of lead (“Pb”) e.g. consider the encapsulantdisclosed in U.S. Pat. No. 8,445,098 (which patent is herebyincorporated by reference). With continued reference to FIGS. 9 and 10as needed in one non-limiting embodiment of the invention, theencapsulant 104 totally covers the top surface 108 and 112 of thecoating stack 32 and 35, of the solar minors 102 and 100, respectivelyand extends past the surface 16 of the substrate 12 toward the surface14 of the substrate 12 and is secured to the peripheral sides or edges114 of the substrate 12 as shown in FIGS. 9 and 10. The top surfaces 108and 112 of the coating stacks 35 and 32 in one non-limiting embodimentof the invention can be totally covered by the encapsulant 104 as shownin FIGS. 9 and 10, or the marginal edge portions of the outer surface108 and 112 of the coating stacks 35 and 32 can be covered by theencapsulant as discussed below. By way of interest and not limiting tothe invention, a prior art encapsulant tested was available from FenziGroup (headquartered in Tribiano, Italy) and was sold under theregistered trademark Solarlux®.

With continued reference to FIGS. 9 and 10, the encapsulant 104 of theinvention includes a bottom or base layer 120 applied over the outerwalls 108 and top surface 108 of the coating stack 35, and/or over theouter walls 110 and top surface 112 of the coating stack 32, and overthe peripheral sides 114 of the substrate 12, a topcoat 122 is appliedover the bottom layer 120 of the encapsulant 104. In one non-limitingembodiment of the invention, the encapsulant includes the bottom layer120 having the ingredients and amounts listed in Table 1, and the topcoat 122 having the ingredients and amounts listed in Table 2.

Suitable methods of application of the encapsulant, include but are notlimited to; (1) curtain eking, (2) spray-coating, (3) flow-coating, (4)draw-down coating and (5) electrocurtain coating, e.g. as disclosed in,but not limited to U.S. Pat. No. 8,557,099, which patent is herebyincorporated by reference. In one non-limited embodiment of theinvention the preferred method of application of the encapsulant 104 iscurtain-coating. The basecoat 120 and the topcoat 122 of the encapsulant104 are applied such that their geometric thicknesses are eachapproximately 1 mil (0.001 inch=25.4 micrometers) in their cured state(i.e. after thermal curing of the encapsulant). However, some range ofthicknesses of each basecoat 120 and topcoat 122 is acceptable, e.g. butnot limited to the range of 0.9 mil to 1.05 mil.

Prior to the application of the encapsulant 104 to the coating stack,e.g. but not limited to coating stack 35 and/or 32, the coating stacksare pretreated to remove any sharp (i.e. “raw” Or “cut”) edges of thecoating stack preferably the sharp edges are blunted or ground, using anabrasive medium such as an abrasive belt or grinding wheel, prior toapplication of the encapsulant 104. This practice is known as“edge-seaming” or simply “seaming”. Edge-seaming of the sharp edges ofthe reflective-coated substrate, prior to application of an encapsulant,ultimately results in a finished mirror having so called “SP”(seamed-then-painted) edges. Edge-seaming is believed to promote somedegree of “wrap-around” of the bottom layer 120 of the encapsulant 104onto the peripheral sides 114 of the substrate 12 thereby limitingdirect exposure of the reflective coating's “sidewalls” to potentiallycorrosive environmental agents that might chemically react with, orotherwise degrade, one or more layers of the reflective coating 22and/or the layer(s) including the Ag or solar reflective layer. Thepractice of edge-seaming is also believed to remove some or all of thereflective coating from the extreme edge/perimeter of the substrate'scoated surface on a microscopic scale. This concept is referred to as“micro-edge-deletion” or “micro-deletion”. A similar practice issometimes followed in order to “edge-delete” Ag-based coatings (e.g.Ag-based low-emissivity and/or solar-control coatings) from theperimeter of coated glass substrates. Such a macroscopic edge-deletionprocess involves removing a macroscopic width (typically severalmillimeters) of a coating from the perimeter of the coated substrate.Such a macroscopic edge-deletion process helps protect the coating fromdirect exposure to environmental agents, which might corrode orotherwise degrade the Ag-based coating 27 (see FIG. 10) and coating 22(see FIG. 9). After the edge-seaming step, the reflective-coatedsubstrate is thoroughly cleaned in any convenient manner, such as usinga flat glass washer, and dried.

Prior to application of the encapsulant 104, a pre-treatment ispreferably applied to the outer walls 110 and the top surface 108 of thecoating stack 32, and the outer walls 106 and top surface 108 of thecoating stack 35 of the solar mirrors 102 and 100, respectively, topromote adhesion of the encapsulant to the outer surfaces of the coatingstacks. The preferred pre-treatment includes a silane-based chemistry;one suitable composition is 0.15 wt. % gamma-Aminopropyltriethoxysilanein deionized (DI) water. The pre-treatment chemistry is sprayed onto theouter surfaces or walls 106 and 110, top surface 108 and 112, of thecoating stacks 25 and 27 and exposed surfaces of the substrate 12 andallowed to well on the surfaces for about 30 seconds residence time,before being thoroughly rinsed off by flooding the surface withdeionized water. immediately following the rinse process, the remainingrinse water is sheeted off the outer surfaces 106 and 110, the topsurfaces 108 and 112, of the coating stacks 32 and 35, respectfully, andexposed surfaces of the substrate 12. The pre-treated coating stacks,the coating stacks 32 and 35, and the substrate 12 are pre-heated toabout 150° F. (66° C.) prior to application of the basecoat or bottomlayer 120 of the encapsulant 104.

A sufficient quantity of the chemistry of the basecoat 120 is applied tothe outer walls or surfaces 106 and top surface 108 of the coating stack35, and outer walls or surfaces 110 and top surface 112 of the coatingstack 32 to achieve a basecoat dry film thickness (OFT) of about 1.1mils (27.94 micrometers) on the finished article. The process parameters(e.g, width of curtain coater's orifice, conveyer line speed ofsubstrate through paint curtain, etc.) for the basecoat applicationprocess are typically empirically adjusted so as to achieve the desiredbasecoat DFT. Immediately following the application of the basecoatchemistry, the substrate travels through a “flash zone” wherein heatcontinues to be applied so as to enable solvents to evaporate from theapplied liquid basecoat layer 120 of the encapsulate 104. A suitabletemperature for this “flash process” is about 150° F. (66° C.). Theapplication of heat in the flash zone also pre-heats the substrate 12 toprepare it to receive the base coat 120 of the encapsulate 104. Aminimum substrate surface temperature of about 120° F. (49° C.),immediately prior to application of the basecoet of the encapsulant, isrecommended, but is not limiting to the invention.

Immediately after removal from the “flash zone” for the topcoat layer122, the encapsulant 104 of the coated substrate is cured in a suitablyvented furnace/oven, which is designed for curing of polymericcoatings/paints on large-area substrates. For any given encapsulatedsubstrate, typical recommended residence time (“ride time”) in thefurnace is 251 seconds. The recommended exit temperature of thesubstrate's encapsulated surface, immediately upon exiting the curingfurnace, is about 280° F. (138° C.). After exiting the furnace, theencapsulated reflective-coated solar mirror is cooled-down, Withreference to FIGS. 9 and 10, and not limiting to the invention, theencapsulated reflective-coated glass substrate was a finished solarmirror having, but not limiting to the invention (1) a substrate (e.g.the glass substrate 12); (2) an MSVD-deposited Ag-based bilayer 28 a and28 b of the reflective coating 27 over one major surface of thesubstrate, e.g. but not limited to surface 16 of the substrate 12; (3)the parting layer 30 on the Ag-based sublayers 28 b; (4) the bilayer 28a over the parting film 30; and (5) the base coat 120 of the encapsulant104 applied over or on the outer wall 106 and top surface 108 of thecoating stack 35 and/or cuter surface 105 and top surface 108 of theMSVD-deposited reflective coating and a top layer 122 applied on thebase coat 120.

Optionally, the bottom surface 14 of the substrate 12 of the finishedsolar mirrors 100 and 102 can be cleaned using an acid-etching processand rinsed/dried prior to unloading. The purpose of such abottom-surface acid-etching process is to remove any contaminants,especially silver-based contaminants that might absorb light andconsequently negatively impact the overall reflectance of the finishedmirror. A solution of ferric chloride (FeCl₃) in deionized water is onesuitable bottom-surface etchant/cleanser.

After being exposed to the etchant, the entire mirror is thoroughlyrinsed with water to remove all traces of etchant from the finishedmirror, and dried using an air knife or similar apparatus.

Finished solar mirrors of the invention, encapsulated in theaforementioned fashion with the encapsulant 104, exhibit acceptableadhesion to the glass substrate 12 as determined using the ASTM 03359Cross-Hatch Adhesion test; a cross-hatch adhesion rating of “4B” orbetter is typical. Similarly, mirrors exhibit an acceptable level ofcure as determined using the ASTM D5402 Solvent Rub Test; 200double-rubs, or more, using a xylene-seaked cloth without visibledegradation of the encapsulant is typical.

Unless indicated otherwise, the above method for preparing the coatingstacks 32 and 35 for the application of the encapsulant 104 is practicedprior to the application of the encapsulant in the following discussionof non-limiting embodiments of the invention.

The discussion is now directed to non-limited embodiments of solarmirrors of the invention having encapsulated coated stacks, e.g. but notlimited to the coating stack 35 (FIG. 9) and coating stack 32 (FIG. 10).These non-limiting embodiments of he invention relate to solarreflecting mirrors, e.g, but not limited to highly-reflective solarmirrors, such as, but not limited to solar mirrors having coating solarreflecting sublayers 28 a and 28 b separated by a parting medium 30(FIG. 9) and solar mirrors having solar reflecting coating, e.g. thesolar reflecting coating 22 of the type shown and discussed in regardsto FIG. 9. The silver reflective coatings 27 and 22 arehighly-reflective to solar radiation and are usually employed forConcentrated Solar Thermal Power (CSTP) and Concentrated Photovoltaic(CPV) applications. CSTP/CPV technologies are sometimes referred to moregenerally as Concentrated Solar Power (CSP) technology. However, itshould be appreciated that the solar mirrors of the invention can beemployed for other applications including, but not limited to, displayapplications, projection applications, lighting applications,entertainment applications, laser applications, directed-energy weaponsapplications, optical applications in general, or any applications whichemploy highly-reflective articles for the solar wavelength spectrum orany subset thereof, or for any application in which the inventiondescribed exhibit suitable optical properties/performance or othersuitable characteristics. As used herein a highly reflective solar film,e.g. but not limited to a silver reflective solar film has a solarreflection in the range of 85 to 95%. With continued reference to FIGS.9 and 10 as needed, the encapsulant 104 of the solar mirror 100 (FIG.9), and/or of the solar mirror 102 (FIG. 10), includes, but is notlimited to, a polyester melamine having the bottom or base layer 120and/or a top layer 122 with selected ones of the layers 120 and 122having metal-resistance-enhancing film or particles of Inconel 600,zinc, aluminum, copper, magnesium, and mixtures, alloys, or combinationsof two or more thereof. In the preferred practice of the invention, themetal selected was Zinc (“Zn”), because in addition to being aresistance-enhancing metal, Zn is a highly electrically conductive metaland can be used electrodeposition coating.

The invention is not limited to the form of the zinc, and the inventioncontemplates Zn in the form of flakes, powder and coated MSVD coatedfilm. In the preferred practice of the invention, Zn was in the form offlakes. The Zn in flake form was selected because samples of encapsulantcoating were made having Zn flakes, Zn powder and zinc film and the zincflakes were the better performer for the electrodeposition of theencapsulant The Zn flakes are identified by the number 124 end shownonly in phantom and only in FIG. 11.

In the practice of the invention, when the Zn flakes are used as aresistance-enhancing metal or a sacrificial cathodic protection, the Znflakes are mixed with the chemistry of the bottom layer 120 and thechemistry of the top layer 122 of the encapsulant 104. When the Znflakes are used to provide a resistance-enhancing metal or a sacrificialcathodic protection, and as a cathode for electrode deposition, the Znflakes are mixed with the chemistry of the base layer 120 of theencapsulant 104. In the following discussion, the Zn flakes are used toprovide a resistance-enhancing metal or a sacrificial cathodicprotection, and as a cathode for electrode deposition; the Zn flakes 124were formulated in a moisture stable binder i.e. the polyester melamineto fit curtain coating application. For a more detailed discussion ofthe zinc flakes in the polyester melamine reference is made to U.S.Published Patent Application No. 201310003206 (Pub. '206), U.S.Published Patent Application No. 2013/0003206 is hereby incorporated byreference.

In the practice of this embodiment of the invention, a Zn-rich polyestermelamine-based topcoat 122 of the encapsulant 104 (FIGS. 9 and 10) isused. For some end-use applications, it may be desirable for thefinished solar mirror to be subjected to certain types ofhigh-temperature processing, such as thermal tempering,heat-strengthening, thermal bending, etc. In that event, thereflective-coated substrate is preferably subjected to suchhigh-temperature processing before application of the encapsulant 104.Although the coating stack 35 of the solar mirror 100 and the coatingstack 32 of the solar mirror 102 can survive high-temperature,processes, it is expected that the polymeric-based encapsulant 104 overthe coating stack 35 and/or will not survive such processes.

Shown in FIG. 11 is a non-limited embodiment of solar mirror 130. Thesolar mirror 130 is the solar mirror 70 or 72 having the encapsulant104. Unless indicated otherwise, the following discussion is applicableto the solar mirrors 70 and 72. With continued reference to FIG. 11, theencapsulant 104 of the invention includes but is not limited to (1) thepolyester melamine-based basecoat 120 impregnated with metalliccorrosion-inhibitive pigments 124 (e.g. metallic Zn flakes 124), and (2)a metallic corrosion-inhibitive pigment free (e.g. metallic flakes124)-free and polyester melamine-based topcoat 122. This encapsulant 104is herein also referred to as “PEM encapsulant”. The solar mirror 130includes, but is not limited to, the MSVD coating stack 32 and/or 35having coating layers 74, 76, 78 and 25 with the PPO coating 26 of thetype disclosed in U.S. Pat. No. 6,016,542 (hereinafter also referred toas “Pat. '542”). Pat '542 is hereby incorporated by reference, in thisdiscussion of the non-limited embodiment of the invention, the basecoat120 of the PEM encapsulant 104 is applied over the layer 25 of the PPO(top surface 108 and/or 112 of the coating stack 32 and 35,respectfully) and the outer walls 108 and 110 of the outer walls of thecoating stack 32 and 35.

As is appreciated by those skilled in the art, the PPO coating or theASVD film 25 or 80 is electrically non-conductive and the Zn flakes 124in the base layer 120 of the PEM encapsulant 104 has a dual function,namely the Zn flakes 124 in the basecoat 120 of the PEM encapsulant 104slows the corrosion of the Ag reflecting coating 22 and 27 by adsorbingmoisture. More particularly, the Zn flakes 124 adsorb moisture passingthrough the topcoat or layer 122 of the PEM encapsulant 104 into thebase coat 120 of the PEM encapsulant 104 and is corroded, after whichthe moisture moves through the base coat 122 of the PEM encapsulant 104and attacks the coating stack 32 and/or 35 in particular the Agreflecting coating 28 and/or 22. The second function of the base coat122 of the PEM encapsulate 104 is to provide a cathode when an e-coatingis applied over the base layer 120 of the PEM encapsulant 104. Theinvention is not limited to the manner in which the e-coat top layer 122is applied, and the top coat 122 of the PEM encapsulant 104 can beapplied in the manners disclosed in U.S. Patent Application PublicationNo. 2013/0003206 (“Pub, '206”). Pub. '206 is hereby incorporated byreference.

A detailed discussion of the PEM encapsulant is provided in Pub. '206and U.S. Pat. No. 8,557,090 (“Pat. '099”). Pub, '206 and Pat. '099,which documents in their entirety are incorporated herein by reference.

Shown in Tables 1 and 2 are the formulation of the basecoat 120(Table 1) and the top coat 122 (Table 2) used in the practice of theInvention to curtain coat the encapsulant 104 on the coating stack 32 asshown in FIG. 10 in accordance to the invention.

The Table 1 below shows the main ingredients as well as generalfunctions of each ingredient:

TABLE 1 Weight Ingredient (grams) Polyester Resin⁽¹⁾ 57.74 Phosphatized4.41 Epoxy⁽²⁾ Melamine⁽³⁾ 45.80 Solvent⁽⁴⁾ 127.9 Flow Additive⁽⁵⁾ 2.17Anti-settling Agent⁽⁶⁾ 23.18 Catalyst⁽⁷⁾ 1.41 Zinc Flake⁽⁸⁾ 381.53Silane A-187 5.00 ⁽¹⁾The polyester resin was POLYMAC HS 57-5776, fromMomentive Specialty Chemicals, which had a solids weight of 85 percentby weight, based on total weight, a hydroxyl number of 178 (based onsolids weight), a hydroxyl equivalent weight of 315 (based on solidsweight), and an acid number of 10 (based on solids weight). ⁽²⁾Thephosphatized epoxy was obtained commercially from PPG Industries, Inc.,under the tradename HEQ-9346. ⁽³⁾The melamine was RESIMENE R-718,commercially available from INEOS Melamines Inc. ⁽⁴⁾The solvent wascomposed of 20.4 percent by weight of SOLVESSO 100 (from Exxon MobilCorporation), 25.8 percent by weight of butyl CELLOSOLVE, and 53.8percent by weight of butanol, in each case based on total weight of thesolvent. ⁽⁵⁾The flow additive was composed of: AL-61-1477, polyolefinoil (18.4% by weight, commercially available from ShamrockTechnologies); AWY-3046. silicon fluid (27.6% by weight commerciallyavailable from Momentive Performance Materials, Inc.); and RCH-8794,polybutyl acrylate (54.0% by weight, commercially available from E. I.du Pont de Nemours and Company), the percent weights being based in eachcase on total weight of flow additive. ⁽⁶⁾The anti-setting agent wascomposed of 53.2 percent by weight of BENTONE SD-2 clay material(commercially available from Elemintis Specialties, Inc.), 30.6 percentAEROSIL 200 fused silica (commercially available from EvonikIndustries), and 4.1 percent by weight of BYK 410 rheology additive(commercially available from BYK USA Inc.), the percent weights eachbeing based on total weight. ⁽⁷⁾The catalyst was NACURE 2500 amineneutralized p-toluenesulfonic acid, commercially available from KingIndustries. ⁽⁸⁾The zinc flakes 124 had the trade designation Z45, whichis commercially available from Purity Zinc Metals, and had a length tothickness ratio of 20:1.

The ingredients of Table 1 were mixed using a coves blade for at least30 minutes until a Hegman rating of 6.5 (on a scale of 1 to 8) wasreached. Solvent (a 1:1 by weight mixture of SOLVESSO 100 and butylCELLOSOLVE) was mixed with the grind paste so as to form a sacrificialcathodic coating composition having a viscosity suitable for sprayapplication.

The sacrificial cathodic coating composition was curtain coated over areflective glass substrate, and allowed to flash at ambient roomtemperature to remove solvent. The applied sacrificial cathodic coatinghad a thickness in the range of 1.0-1.2 mils.

A polyester melamine coating composition (free of lead) for use as theouter organic polymer coating top coat 122 of the encapsulant 104 wasprepared as shown in Table 2 below:

TABLE 2 Weight Ingredient (grams) Polyester Resin⁽⁹⁾ 120.90 Phosphatized7.97 Epoxy⁽²⁾ Melamine⁽³⁾ 18.19 Solvent⁽⁴⁾ 38.1 Flow Additive⁽⁵⁾ 2.17Catalyst⁽⁷⁾ 0.47 TiO₂ 89.8 ⁽⁹⁾The polyester resin was obtainedcommercially from PPG Industries, Inc. under the designation HP 73-5480SP3, and had a solids weight of 65 percent by weight, based on totalweight, a hydroxyl number of 89.2 (based on solids weight), a hydroxylequivalent weight of 628.9 (based on solids weight), and an acid numberof 3.8 (based on solids weight).

The Ingredients of Table 2 were mixed using a cowls blade for at least30 minutes until a Hegman rating of 6.5 (on a scale of 1 to 8) wasreached. Solvent (a 1:1 by weight mixture of SOLVESSO 100 and butylCELLOSOLVE) was mixed with the grind paste so as form an outer organicpolymer coating composition having a viscosity suitable for sprayapplication.

The lead-free outer organic polymer top coat 122 prepared from the grindpaste of Table 1 was curtain coated, using mini curtain coaters, overthe previously applied sacrificial cathodic coating i.e. over the basecoat 120. The sacrificial cathodic coating i.e. the base coat 122 andthe outer organic polymer coating i.e. the top coat 122 were togethercured at a temperature of 320° F. for 4 minutes, 11 seconds in aHedinair oven (not shown). The outer organic polymer coating i.e. topcoat 122 had a thickness of 1 mil (25 microns).

In one non-limiting embodiment of the invention, the coating processinvolves cleaning the glass substrate 12 having dimensions of 6 inch×12inch×3.3 mm NSVD mirror with Di water, then pretreating it with A1100Mane at ratios of 5% in (25% isopropyl alcohol and 75% water). The glasssubstrate 12 is then preheated to 150° F. for 1 minute prior toapplication of the basecoat 120 (see FIG. 11). The basecoat 120 was thenflashed at 150° F. about 1 minute to remove some of the solvent in thebase coat 120 and the top coat 122 applied. The combination is thencured together in the Hedinair oven for 3 minutes 20 seconds. Cure isverified by using >100 double MEK rubs. The samples are then cut toexpose edges and tested on screening tests like CASS.

The base layer 120 and the top layer 122 of the PEM encapsulant 104 areapplied on top of the MSVD-deposited solar-reflective coating stack 32or 35 shown in FIG. 11. Suitable methods of application of theencapsulant 104 include, but are not limited to: (1) curtain-mating, (2)spray-coating, (3) flow-coating, (4) draw-down coating and (5)electrocurtain coating. The preferred method of application iscurtain-coating.

The base coat 120 and the topcoat 122 of the PEM encapsulant 104 areapplied such that their geometric thicknesses are each approximately 1mil (0.001 inch=25.4 micrometers) in their cured state (i.e. afterthermal curing of the encapsulant). However, in the practice of theinvention it is expected that some range of thicknesses of each layer isacceptable, e.g. but not limited to 0.5 mil to 2 mil.

Prior to application of the pre-treatment and encapsulant, any sharp(i.e. “raw” or “cut”) edges of the reflective-coated substrate areremoved and the surfaces cleaned as discussed above.

Further, prior to application of the Pem encapsulant 104, apre-treatment is preferably applied to surface 131 of the coating layer80. The coating layer 80 is a protective overcoat of Si (85%)-Al (15%)oxide layer to protect the solar reflective coating stack 32 and 35 (seeFIG. 11). The pretreatment of the surface 131 promotes adhesion of thePam encapsulant 104 to the surface 131 of the coating layer 80. Theinvention contemplates cleaning the outer surface of the coating stacks32 and 35 to enhance the adhesion of the mating stack and the base layer120 of the encapsulant 104 of the solar cell 130. A detailed discussionof the PPO coating 25 is provided in U.S. Pat. No. 8,445,098,

The invention is not limited to the adhesion promoter that can be usedin the practice of the invention, and any of the known adhesionpromoters can be used in the practice of the invention, in onenon-limiting embodiment of the invention A preferred pre-treatmentincluded but is not limited thereto a silane-based chemistry onesuitable composition is 5 wt. % gamma-Aminopropyltriethoxysilane ontotal solution eight in a pre-mixed matrix of 25 wt. % isopropanol: 75wt. % deionized water; commercially available forms of this sanechemistry are Silquest® A-1100 available from Momentive Corporation orGeneral Electdo Corporation. The pre-treatment chemistry is sprayed ontothe coating column or stack 32 and/or 35 and allowed to dwell on thatsurface for 30 seconds residence time, before being thoroughly rinsedoff by flooding the surface with deionized water. Immediately followingthe rinse process, the remaining rinse water is sheeted off the coatingstack 32 and/or 35 using an air knife or similar apparatus. Thepre-treated coating stack is then pre-heated to about 200° F. (93° C.)prior to application of the PEM basecoat 120.

The invention is not limited to the method of applying the PEM basecoat104 chemistry and the methods include but are not limited,curtain-coating, spray-coating, flow-coating, electrodeposition coatingand draw-down coating. For application via a curtain-coating process,the as-received Zn-PEM basecoat chemistry is reduced to the recommendedapplication viscosity (15-23 seconds, #3 Zahn cup) using a suitablesolvent such as 2-Butoxyethanol (also known as “butylcellosolve”),xylene, Solvesso® 100 solvent, similar solvents, or combinationsthereof. A sufficient quantity of the basecoat chemistry is applied tothe reflective-coated substrate so as to achieve a basecoat dry filmthickness (DFT) of about 1.1 mils (27.94 micrometers) on the finishedarticle. The process parameters (e.g. width of curtain coater's orifice,conveyer line speed of substrate through paint curtain, etc.) for thebasecoat application process are typically empirically adjusted so as toachieve the desired basecoat DFT. Immediately following the applicationof the PEM basecoat chemistry, the substrate moves through a furnacewherein heat continues to be applied so as to enable solvents toevaporate from the applied liquid basecoat layer. The area in which thesolvent is removed is called for purposes of clarity as “flash zone”.

The application of heat in the flash zone also pre-heats the substrateto prepare it to receive the top chemistry of the PEM encapsulant 104chemistry; a minimum substrate surface temperature of about 120° F. (49°C.), immediately prior to application of the topcoat 122 of the PEMencapsulant 104.

A variety of methods are acceptable to apply the PEM topcoat 122chemistry including, but not limited to, curtain-coating, spray-coating,flown acing, and draw-down coating. For application via acurtain-coating process, the as-received PEM topcoat chemistry 122 isreduced to a recommended application viscosity (15-23 seconds, #3 Zahncup) using, a suitable solvent such as 2-Butoxyethanol (also known as“butylceilosolve”), xylene, Solvesso® 100 solvent, similar solvents, orcombinations thereof. A sufficient quantity of the PEM topcoat chemistryis applied to the substrate so as to achieve a topcoat dry filmthickness (DFT) of about 1.0 mils (25.4 micrometers) on the finishedarticle. The process parameters (e.g., width of curtain coater'sorifice, conveyer line speed of substrate through paint curtain, etc.)for the topcoat application process are typically empirically adjustedso as to achieve the desired topcoat DFT. Immediately following theapplication of the topcoat chemistry of the Zn-PEM encapsulant, thesubstrate optionally travels through a second “flash zone” so as topermit so tints to evaporate from the applied liquid topcoat layer.

Immediately after emerging from any “flash zone” for the topcoat layer122 of the PEM encapsulant 104, the coated substrate is cured in asuitably vented furnace/oven which is designed for curing of polymericcoatings/paints on large-area substrates. For any given substrate coatedwith the PEM encapsulant 104, typical recommended residence time (aleknown as “ride time”) in the furnace is about 251 seconds. Therecommended exit temperature of the substrate's encapsulated surface,immediately upon exiting the curing furnace, is about 280° F. (138° C.).After exiting the furnace, the encapsulated reflective-coated glass ispermitted to cool-down in preparation for unloading from themanufacturing line. At this point, the solar mirror constitutes afinished mirror including: (1) a substrate (e.g. a glass substrate 12),(2) an MSVD-deposited Ag-based reflective coating on one major surfaceof the substrate (coating column or stack 166), and (3) the PEMencapsulant 104 applied on top of the MSVD-deposited reflective coatingstack 32 or 35.

Optionally, the bottom surface of the finished mirror, e.g. the surface14 of the substrate 12 (see FIG. 11) can be cleaned using anacid-etching process and rinsed/dried prior to unloading. The finishedmirror is then stored and shipped in any usual manner.

Finished solar mirrors, encapsulated in the aforementioned fashion withthe PEM encapsulant 104, exhibit acceptable adhesion to the substrate asdetermined using the ASTM D3359 Cross-Hatch Adhesion test: a cross-hatchadhesion rating of “4B” or better is typical. Similarly, mirrors exhibtan acceptable level of cure as determined using the ASTM D5402 SolventRub Test; 100 double-rubs, or more, using a methyl ethyl ketone-soakedcloth without visible degradation of the encapsulant is typical.

Non-Limiting Embodiments of the Invention using PEM Encapsulant onCoating Stacks without a PPO Layer

As is appreciated by those skilled in the art, the PRO layer 25 of thecoating stacks 32 and/or 35 has a sheet resistance value greater thanmega ohm/square. As discussed above, for eleotrodeposition coatings,electrical connection to the outer surface or top surface 108 of the PPOlayer 25 of the coating stack 35 of the solar mirror 100 (see FIG. 9),and electrical connection to the outer surface 112 of the coating stack32 of the PRO layer 25 of the solar mirror 102 (see FIG. 10), isaccomplished by adding electrically conductive material to the baselayer 120 of the PEM encapsulant 104. In the practice of the invention,zinc flakes 124 were added to the base layer 120 (see Table 1) of thePEM encapsulant 104 because in addition to zinc providing an electricalconduction, zinc is also a metal-resistance-enhancing film. The coatingstack 32 and/or 35 without the PRO layer 25 has the surface 78A of thelayer 78 (FIG. 11) available for electrical connection. The surface 78Ais expected to have a sheet resistance value less than 0.5 megaohm/square. In the non limited embodiments of the invention discussedbelow one or both of the layers 120 and 122 of the PEM encapsulant 104covering the surface of the coating stack 32 and/or 35 is free of lead(see Tables 1 and 2), With continued reference to FIGS. 9 and 10 asneeded, the encapsulant 104 of the solar mirror 100 (FIG. 9), and/or ofthe solar mirror 102 (FIG. 10), includes, but is not limed to, apolyester melamine having the bottom or base layer 120 and/or a toplayer 122 with selected ones of the layers 120 and 122 havingmetal-resistance-enhancing film or particles Inconal 600, zinc,aluminum, copper, magnesium, and mixtures, alloys, or combinations oftwo or more thereof. in the preferred practice of the invention, themetal selected was Zinc, because in addition to being aresistance-enhancing metal, Zn is a highly electrically conductive metaland can be used electrodeposition coating, in either case the absence ofthe PPO layer 25 allows reduction in the level of costly Zn flakes 124used in the base coat 120 of the PEM encapsulant 104 by eliminating thePPO layer 23 while maintaining the same or improving the level ofcathodic protection to the solar reflective surface 22 and/or 27.

As can be appreciated the formulation for the base layer 120 of the PEMencapsulant 104 is found on Table 1 and the formulation for the toplayer 122 of the PEM encapsulant 104 is found on Table 2. The presenceof the Zn flakes 124 listed is Table 1 is optional and is discussed indetail below.

In the following non-limiting embodiments of the invention, a solarmirror, e.g., but not limited to the solar mirror 130 of FIG. 11 has acoating stack without the PPO layer 26 and has the two layer encapsulant104 (see FIG. 11). As mentioned above the PPO layer 26 provides chemicaland mechanical protection for the mayor surface 78A of the film orcoating 78 of the coating stack 32 and 35. With or without the presenceof the PPO layer 25, the PEM encapsulant 104 provides the chemical andmechanical protection for the major surface 75A and the coating stack 32and 35. The protection provided by the PPO layer 25 to the coating stack32 and/or 35 is now provided by the PEM encapsulant 104. Moreparticularly, shown in FIG. 11 is solar mirror 130 having the MSVDcoating stack 32 or 35 having layers 24, 76 and 78, with solarreflecting coating 22 or 27. The base coat 120 of the PEM encapsulant104 having the Zinc flakes 124 is applied over the top surface 78A ofthe layer 78 and the outer walls 108 and 110 of the coating stack 32 and35 of the reflective article or solar mirror 130.

The Zn flakes 124 in the bottom layer 120 and the top layer 122 of thePEM encapsulant 104 has the function of slowing the corrosion of the Adlayer 27 and/or 22 by adsorbing moisture in the atmosphere passing intothe top layer 122 and bottom layer 120. More particularly, the Zn flakesare used to provide a resistance-enhancing metal or a sacrificialcathodic protection, and as a cathode for electrode deposition; the Znflakes 124 were formulated in a moisture stable binder i.e. thepolyester melamine to fit curtain coating application For a moredetailed discussion of the zinc flakes in the polyester melaminereference is made to U.S. Published Patent Application No. 2013/0003206(Pub. '206)

As can be appreciated, the invention contemplates further reductionsand/or modifications to the solar mirror 130. For example and notlimiting to the invention, the bottom layer 120 can have the zincflakes, and the top layer 122 can be free of Zinc flakes as shown inFIG. 11, or both the layers 120 and 122 can be free of Zinc flakes, orboth layers 120 and 122 can have the zinc flakes. The encapsulant 104can have only one layer which can be any thickness.

As can be appreciated, the invention contemplates additionalnon-limiting embodiments of the invention by alternating the componentsof the solar mirror 130 shown in FIG. 11. Unless indicated otherwise themodifications to the solar mirror 130 discussed below can be made to thesolar mirrors discussed above, e.g. but not limited to solar mirrors 5(FIG. 1), 7 (FIG. 3), 70, (FIG. 5), 72 (FIG. 6), 100 (FIG. 9), 102 (FIG.10), 130 (FIG. 11) and 134 (FIG. 13, discussed below).

Non-limited embodiments of the invention include but are not limited to:

-   -   Solar Mirror A includes but is not limited to the coating stack        32 or 36; the bottom layer 120 and the top layer 122 of the PEM        encapsulant are each without metal-resistance-enhancing film or        particles, e.g. Zn flakes 124. The layer 122 can be electro        deposited because surface 78A of the coating stack 32 or 35 is        electrically conductive.    -   Solar Mirror B includes but is not limited to no        metal-resistance-enhancing film or particles e.g. Zn flakes 124        Zn in the bottom layer 120, and metal-resistance-enhancing film        or particles, e.g. Zn flakes 124 in the top layer 122, of the        PEM encapsulant. Preferably but not limiting to the invention,        the layers 120 and 122 of the PEM encapsulant can be deposited        by e-coating. Instead of using zinc, the invention contemplates        using other metal-resistance-enhancing film or particles.    -   Solar Mirror C includes but is not limited to        metal-resistane-enhancing film or particles, e.g. Zn flakes 124        in the bottom layer 120 and in the top layer 122 of the PEM        encapsulant. Metal-resistance-enhancing film or particles other        than Zn can be used.

Solar Mirror D includes metal-resistance-enhancing film or particles,e.g. Zn flakes 124 in the bottom layer 120, and no Zn in the top layer122, of the Zn-PEM encapsulant. The layer 122 can be electro-coated.Metal-resistance-enhancing film or particles other than Zn can be usedin the practice of the invention.

Preferably but not limiting to the invention, the coaling films andlayers of Solar Mirrors A-D can be applied by any appropriate coatingprocess including, but not limited to slot, curtain coating, end/orelectro deposition.

The invention is not limited to the manner in which the e-coat top layer122 is applied, and the top coat 122 of the PEM encapsulant 104 can beapplied by flow coating in the manner disclosed in U.S. PatentApplication Publication No. 2013/0003206 (“Pub. '208”), whichpublication is hereby incorporated by reference. As can be appreciatedthe addition of Zn flakes 124 to aid in the e-coating adds additionalcosts to the PEM-encapsulant 104 of the coating stack. In anothernon-limited embodiment of the invention, the reduction in the use of Znis provided. The Zn flakes 124 ate added to the base layer 120 of thePEM encapsulant 104 to provide a conductive surface for e-coating. Theelimination of the PPO layer 25 reduces the amount ofmetal-resistance-enhancing film or particles, e.g. Zn flakes 124 neededin the PEM encapsulant 104 by about 50%. The solar mirror 130 of theinvention shown in FIG. 11 now includes the coating stack, and the baselayer of the PEM encapsulant 104 having reduced amounts of Zn. It isestimated that the Zn content in this embodiment Of the invention canhave a Zn flake reduction of 50%.

In either case the absence of the insulating PPO layer 25 should alsoallow reduction in the level of costly Zn flakes in the base coat of thePEM encapsulant by eliminating the PPO layer 25 while maintaining thesame (or improving) the level of cathodic protection to the silver.

U.S. Pat. No. 8,557,099 (Pat. '099) discloses en apparatus for andmethod of coating a reflective article, e.g. a solar mirror with anelectrodeposition coating.

Previously second surface solar mirrors have typically been encapsulatedwith two or even three-layer systems that include first applying acorrosion resistant basecoat, followed by a protective topcoat. Thesecan be applied by traditional wet coating methods such as curtaincoating.

If the basecoat is electrically conductive such as the basecoat of thepartially organic metal containing basecoat 120 of the PEM encapsulant104, the to e.g. but not limited to the topcoat 122 applied over thebasecoat 120 of the PEM encapsulant 104 can be an electrodepositiontopcoat, e.g. of the type disclosed in Pat. '099, which provides manyadditional advantages such as better uniformity, thickness control,higher transfer efficiency, less waste, low volatile organic content,etc. However, if the top layer of the reflective structure as describedin Pat. '099 is an insulating material then a conductive basecoat isstill required in this case to perform the electrodeposition easily. Itthe reflective mirror film is considered so that there is no significantinsulating film on the top surface of the coating stack, the mirror canbe encapsulated by direct electrodeposition of an electrodepositionpaint formulation without the need for an electrically conductivebasecoat, e.g. but not limiting to the invention the base coat 120 ofthe encapsulant 104.

This single layer PEM encapsulant coating provides significant costreduction and potential process advantages including much moreflexibility in manufacturing design, such as the possibility ofinstalling a cascade electrodeposition coater of the type disclosed inPat. '099 at a MSVD production facility without requiring a basecoatapplication line as well.

With reference to FIG. 12 there is shown a non-limiting embodiment of asolar mirror 150. The soar mirror 150 includes the substrate 12, theunderlayer 24, and the solar reflecting layer 22 or 27. In place of theconductive encapsulant bash coat 120 of the PEM encapsulant 104 is thesolar reflecting layer 22 or 27 of the coating stack 32 or 35 withoutthe PPO layer 25. The function of the encapsulant basecoat 120 isreplaced with an electrodeposited encapsulant 152 of the type disclosedin Pat. '099, or the solar reflecting layer 22 or 27 of the coatingstack 32 or 35 without the PPO layer 25.

The electredeposited encapsulant 152 of the solar mirror 150 wasfabricated and tested and passed the CASS Fog Test.

With reference to FIG. 13 it can now be appreciated that based on theforgoing, solar mirror 156 shown in FIG. 13 can be reduced to thesubstrate 12, the underlayer 24, the solar reflective coating 22 or 27and the electrodeposited encapsulant 152.

Non-Limiting Embodiments of the invention Using Framed PEM Encapsulanton Coating Stacks with a PPO Layer

The following discussion makes reference to the solar mirror 160 shownin FIGS. 14 and 15, however, it is understood that the discussion unlessindicated otherwise is applicable to all the solar mirrors discussedherein. With reference to FIG. 15, the solar mirror 160 includes thecoating stack 32 or 35 applied to the surface 16 of the substrate 12.The coating stacks 32 and 35 each include the underlayer 24 over thesurface 16 of the substrate 12; the solar reflecting coating 27 or 22over the underlayer 24, the layers 76 and 76 over the solar reflectingcoating 27 or 22, end the PPO layer 25 over the coating layers 76 and78. As can now be appreciated, to prevent or reduce corrosion of thesolar reflecting coating 27 and 22, and other films of the coatingstacks 32 and 35, the coating stack includes the PPO layer 25 and thePEM encapsulation systems discussed above.

During the CASS testing it was noted that the position that corrosion ofthe coating stack 32 and 35 usually begins at the outer walls of thecoating stack 35 and the outer walls 110 of the coating stack 32, andmoves inward, seldom beginning on the major surface, e.g. the topsurface 108 of the PPO coating 25. It was concluded that the centerportion 164 of the top surface 108 of the PPO layer 25 does not have tohe coated with the base layer 120 and the zinc flakes 124 of thePEM-encapsulant 104. As can now be appreciated, eliminating the basecoat 120 and the zinc flakes 124 therein of the PEM-encapsulant 104 overthe center portion 164 of the PPO layer 25 provides a significantreduction in the cost of materials and manufacturing time.

As may be recalled, in the above discussion, the base layer 120 havingZinc flakes was applied over the top surface 108 of the PPO layer 25 sothat the top layer 122 of the PEM-encapsulant 104 can be e-coated to thebottom layer 120 of the PEM-encapsulant 104.

Shown in FIGS. 14 and 15 is the solar mirror 160. The solar mirror 160has the basecoat 120 of the PEM encapsulant 104 on the marginal edges166 of the PPO layer 25 and extends over the edges or outer walls 110 ofthe coating stacks 32 and 35. The top coat 122 of the PEM-encapsulant104 is applied over the base layer 120 and over the center portion 164of the PPO layer 25. The center portion 164 of the surface of the PPOlayer 25 is blocked off during the application of the Zn basecoat 120 inany convenient manner. The topcoat 122 can be applied by selection ofone of the coating process discussed herein.

By applying the Zn basecoat 120 to the peripheral edges of the coatingfilms and the marginal edges of the PPO film 25, and applying the topcoat 122 over the Zn based coat and the exposed PPO surface, sufficientcorrosion protection is obtained to pass the CASS Fog Test.

The invention is not limited to the width of the Zn basecoat applied tothe marginal edges of the PPO layer 25. A sample for the CASS Fog Testhad a length of 3 feet and a width of 2 feet. The Zn base coat 120 onthe marginal edges of the PPO layer 25 had a width in the range of 1-2centimeters. The sample passed the CASS Fog Test. Optionally a top coat122 can be applied over as the base coat 120 and the exposed surface ofthe PPO layer 25 for added protection.

The width of the base 120 overlaying the marginal edges of the PPO layer25 is generally in the range of greater than zero to 5 inches, greaterthan zero to 4.5 inches, greater than zero to 4.0 inches, greater thanzero to 3.5 inches greater than zero to 3.0 inches, and greater thanzero to 2.5 inches.

In another test, two samples of MSVD mirror approx. 5×6 inches weremasked in the center and coated by drawdown with the basecoat 120,flashed at 245° F., and top coat 122 by drawdown after removing thecenter mask. After cure, 1 inch was cut off of each side of the sample,leaving a 3×4 inches size sample with four painted then cut edges and acenter area with no basecoat 120, only the topcoat 122. After 120 hoursof CASS Fog Test exposure, there was no corrosion along any of the cutedges nor any on the center of the face that was protected by onlytopcoat of the encapsulation. By contrast, samples having the topcoat122 but no base coat 120 of the PEM encapsulant 104 all failed the CASSFog Test by 120 hours.

The advantages of this embodiment of the invention are (1) the use ofanticorrosion coating to cover the edges of the coating stack and themarginal edges of the outermost sheet by aroller/spray/print/electrocoat as disclosed in Pat. '099 and Pub. '206or similar methods, in contrast to many gallons of coating required toestablish a process such as curtain coating for full-surface coverage ofthe outermost sheet, (2) covering only a small percentage area of themirror near the edges greatly reduces material cost, and (3) reductionin the weight of the solar minor.

The invention can be practiced to make second surface mirrors asdiscussed shove, hut can also be practiced to make first surface mirrorsif the protective overcoat is transparent or if the first surface mirroritself has sufficient durability to survive with only edge protection.By applying the Zn basecoat (anticorrosion coating) to the edges of themirror only, sufficient cathodic protection is obtained to prevent onsetof corrosion, while potentially significantly reducing cost and weightof the two layer encapsulation system.

In the discussion of the non-limited embodiments of the invention, thecoating stack was applied to the second surface of the substrate, thesurface facing away from the sun. In this manner the sun's rays passthrough the first and second surfaces of the substrate. The invention;however, is not Writing thereto, and the coating stack having the PEMencapsulant can be mounting the first surface of the substrate, e.g. thesurface facing the sun by using a transparent encapsulant, e.g. removingthe color pigment from the materials of the encapsulant, in this manner,the sun's rays pass through encapsulant to the solar reflecting film andreflected back through the encapsulant.

The invention is not limited to the embodiments of the inventionpresented and discussed above which are presented for illustrationpurposes only, and the scope of the invention is only limited by thescope of the following claims and any additional claims that are addedto applications having direct or indirect linage to this application.

1. An article for reflecting solar energy, comprising: a coating stackcomprising: solar reflecting films and metal oxide films, the coatingstack applied on a major surface of a glass substrate, and a protectiveovercoat, the protective overcoat comprising a first and a secondsurface, wherein the first surface of the protective overcoat isdisposed toward the solar reflective films and metal oxide films; and apolymer encapsulant over outer wall surfaces of the coating stack, thesecond surface of the protective overcoat and over peripheral edges ofthe coated article, the encapsulant comprising a base layer, a top layerand metallic corrosion-inhibitive material in the base layer.
 2. Thearticle according to claim 1, wherein the metallic corrosion-inhibitivematerial is zinc flakes and the zinc flakes are in the top surface ofthe coating stack and the outer wall surfaces of the coating stack arecovered with the base layer and the base layer is covered with the toplayer.
 3. The article according to claim 1, wherein marginal edgeportions of the top of the coating stack and the outer walls of thecoating stack are covered with the base layer and the base layer definesan uncoated area on the top surface of the coating stack, and the toplayer overlays the base layer and the uncoated area of the top surfaceof the coating stack.
 4. The article according to claim 3, wherein thebase layer of the encapsulant covers 2 centimeters of the marginal edgesof the surface of the coating stack.
 5. The article according to claim2, wherein the zinc flakes are in one of the following groups, Group (1)zinc flakes are only in the base layer, Group (2) zinc flakes are onlyin the top layer, and Group (3) zinc flakes are in the top layer and thebase layer.
 6. The reflective article according to claim 1, wherein thecoating stack comprises a corrosion-resistance-enhancing andUV-absorbing layer.
 7. An article for reflecting solar energy,comprising: a coating stack secured to major surface of a glasssubstrate, the coating, comprising a solar reflecting layer, whereinsurface of the coating stack spaced from the substrate is electricallyconductive, and a polymer encapsulant over outer wall surfaces of thecoating stack, the encapsulant comprising a layer e-coated to outersurface of the coating stack, and zinc flakes in a base layer.
 8. Thereflective article according to claim 7, wherein the base coat coversthe marginal edges of outer surface of the coating stack.
 9. Thereflective article according to claim 8, wherein the encapsulantcomprises a top coat wherein the top coat of the encapsulant covers thebase coat and exposed surface portions of the outer surface of thecoating stack.
 10. The reflective article according to claim 7, whereinthe base coat covers the outer surface of the coating stack and theencapsulant comprises a top coat positioned over the base coat.
 11. Thereflective article according to claim 7, wherein the base coat of theencapsulant comprises a polyester melamine having electric conductive,moisture absorbing metal flakes.
 12. The reflective article according toclaim 7, wherein encapsulant comprises a top coat wherein the top coatcomprises a TiO2 polyester melamine to provide ultraviolet mechanicalabrasion resistant coverage.
 13. The reflective article according toclaim 7, wherein a permanent protective overcoat is positioned over thesolar reflecting layer.
 14. The reflective article according to claim 7,wherein the coating stack further comprises an intermediate film betweenthe substrate and the solar reflecting layer.
 15. The reflective articleaccording to claim 7, wherein the coating stack consists essentially ofthe glass substrate, the solar reflecting layer, and an intermediatefilm between the substrate and the solar reflecting layer.
 16. A solarmirror comprising: a glass substrate, a coating stack having a centersurface and at least one marginal edge of an outer surface, wherein thecoating stack is secured to a major surface of the glass substrate andcomprises solar reflecting films and metal oxide films; and a polymerencapsulant comprising a top layer, and a base layer comprising metalliccorrosion-inhibitive material, wherein the polymer encasement covers theat least one marginal edge of the outer surface of the coating stack.17. The solar mirror according to claim 16, wherein the coating stackfurther comprises a protective overcoat, the protective overcoatcomprising a first and a second surface, wherein the first surface ofthe protective overcoat is disposed toward the solar reflective filmsand metal oxide films.
 18. The solar mirror according to claim 16,wherein the top layer of the polymer encapsulant covers the centersurface of the coating stack.
 19. The solar mirror according to claim18, wherein the top layer of the polymer encapsulant contacts the centersurface of the coating stack.
 20. The solar mirror according to claim16, wherein polymer encapsulant comprises at least one of the followinggroups, Group (1) zinc flakes are only in the base layer, Group (2) zincflakes are only in the top layer, and Group (3) zinc flakes are in thetop layer and the base layer.